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Cater to your tastebuds and discover the ultimate mushroom onion recipe with these perfectly roasted onions and mushrooms. This easy-to-make dish boasts a harmonious blend of caramelized onions and tender mushrooms in a rich garlic butter sauce, delivering an irresistible taste that perfectly enhances steak, pasta, chicken, and more! Best of all, you’ll need just 5 minutes of hands on prep to make them.

“Made this recipe with Portobello mushrooms, did not have enough pearl onions so substituted sliced shallots. The best baked mushrooms ever. I appreciated all the mushroom pro tips and the nutrition information.”

– Mary Anne
Overhead photo of roasted onions and mushrooms with garlic butter in a white bowl.

Update: This recipe was originally published in December 2014. I made updates to the post below to include more information about roasting mushrooms and onions.

Table of Contents

About this recipe for mushrooms and onions

Discover a culinary gem with this mushroom onion recipe, featuring roasted onions and mushrooms that deliver a burst of flavor in every bite. This dish is a celebration of rich, earthy mushrooms paired with sweet, caramelized onions, all perfectly roasted to achieve a delightful texture. Tossed with a rich, luscious garlic butter sauce infused with white wine, this is a savory, umami-packed side dish that’s as indulgent as it is satisfying. Whether you’re serving it alongside steaks, a hearty main course, or enjoying it on its own, this mushroom with onion recipe promises a taste experience that’s equal parts gourmet and comforting.

But, not only are these roasted onions and mushrooms incredibly delicious, but they’re also remarkably easy to prepare. With minimal ingredients, straightforward steps, and 5 minutes of hands-on preparation, you can have a sophisticated side dish ready in no time. Its versatility makes it an ideal choice for any meal, from casual family dinners to festive gatherings. Get ready to elevate your dining experience and impress your guests with this simple yet deliciously versatile dish!

If you love mushrooms be sure to check out these fan-favorite recipes next: Sautéed Mushrooms, Marsala Mushroom Sauce, Easy Mushroom Spaghetti Sauce, Mushroom Orzo Risotto Recipe, and Marinated Mushroom Recipe.

Why you’ll love this recipe

  • Exquisite Flavor Blend! This recipe combines earthy mushrooms with sweet small onions and a rich wine and garlic butter sauce. The result is a depth of flavor that outshines typical veggie side dishes.
  • Simple Preparation: With straightforward instructions and readily available ingredients, this onion mushroom dish is easy to prepare, making it perfect for both weeknight dinners and special occasions.
  • Versatile Side Dish: The recipe’s balanced flavors and elegant presentation make it a versatile addition to any meal, from casual family dinners to festive gatherings, pairing beautifully with a variety of main courses.
  • Gourmet Touch at Home: Experience restaurant-quality results without leaving your kitchen. The combination of wine and garlic butter elevates this recipe to a gourmet level, offering a luxurious touch that’s sure to impress every time.
Close-up photo of garlic butter mushroom with onion on a large baking sheet.

Ingredients you’ll need to make these onions and mushrooms

  • Mushrooms – I prefer cremini mushrooms (also known as baby bellas), white button mushrooms for rich, earthy flavors and a hearty texture. Be sure to select firm mushrooms with no blemishes or wrinkles for the best results.
  • Frozen Pearl Onions – Adds a sweet and delicate flavor with a beautifully tender texture. Be sure to fully defrost the small onions before using.
  • Olive Oil: You’ll need a high quality olive oil for roasting to create a crispy exterior.
  • Salt and Black Pepper: To bring out all the flavors of the mushrooms and onions.
  • Butter: You’ll need unsalted butter to make the garlic butter sauce.
  • White Wine: Select a good, dry white wine that you enjoy drinking as this adds complexity and a hint of acidity to the butter sauce.
  • Garlic: Provides a robust, aromatic flavor that perfectly complements the onions and mushrooms.
  • Fresh Herbs: A combination of fresh thyme and fresh oregano lend fragrant, herbal notes that elevate the overall profile of this dish.

Recipe variations

  • Balsamic Mushrooms Onions: Drizzle a tablespoon of balsamic vinegar over the veggies during the last 5 minutes of roasting for a slightly sweet and tangy flavor.
  • Spicy Variation: If you’re a lover of fiery heat, add a pinch of red pepper flakes to the olive oil before roasting.
  • Parmesan Breadcrumb Topping: For a richer flavor, mix a little freshly grated parmesan and breadcrumbs together and then sprinkle over the mushrooms and onions during the last 5 minutes of baking.
Angled photo of garlic butter onions with mushrooms in a white serving bowl.

How to make roasted onions and mushrooms

This garlic butter onion and mushroom recipe is incredibly easy to make! With just a handful of ingredients and a large, rimmed baking dish, you can prepare restaurant-quality side dish at home. Here’s how:

  1. Preheat oven to 425 degrees F.
  2. Season mushrooms:  Place mushrooms and onions on a large, rimmed baking dish. Toss with oil and season with a pinch of salt and pepper. Arrange the vegetables in a single layer, with the mushrooms facing stem side down. Add 4 sprigs of fresh thyme and 2 sprigs of rosemary to the baking dish.
  3. Partially roast:  Place mushrooms and onions in the oven. Roast for 15 minutes or until lightly browned.
  4. While the mushrooms are roasting, make the butter sauce:  In a large, microwave-safe liquid measuring cup, combine butter, wine, garlic, thyme and oregano. Season with ¼ teaspoon salt and 1/8 teaspoon pepper. Microwave at 1 for 1 minute. Stir and microwave again for 1 ½ in 30 second increments. (SEE NOTES)
  5. Toss with butter and finish roasting:  Remove mushrooms and onions from the oven. Drizzle the butter sauce over the vegetables and gently toss or stir to coat. Continue roasting for 5-10 minutes or until mushrooms are browned and tender. Taste and adjust for seasoning with salt and pepper.
  6. Serve:  Transfer mushrooms and onions to a serving dish. Drizzle with butter sauce from the baking dish. Garnish with fresh herbs and lemon if using. Enjoy!

Expert tips for the best success!

  • Preheat the Oven Properly: Ensure your oven is preheated to 424°F for optimal roasting. A hot oven helps achieve a crispy exterior while keeping the inside tender.
  • Clean and Prepare Ingredients Correctly: Clean the mushrooms with a damp cloth and trim the stems so they are flush with the caps. For pearl onions, make sure they are defrosted and ready to roast.
  • Season Generously: Don’t skimp on sea salt and freshly ground black pepper. Generous seasoning is crucial for bringing out the natural flavors of the roasted onions and mushrooms.
  • Avoid Overcrowding: Arrange the mushrooms and onions in a single layer on the baking pan, ensuring they are not overcrowded. Proper spacing allows for even roasting and prevents steaming.
  • Toss with Garlic Butter Midway: Be sure to remove the veggies from the oven and toss them with the garlic butter about halfway through roasting. This ensure even browning and caramelization on all sides.
  • Garnish with Fresh Herbs: Add a sprinkle of freshly chopped herbs (I like thyme or oregano) after roasting for a burst of fresh flavor. Fresh herbs provide a vibrant contrast to the rich, roasted taste.

Step-by-step photos: making this recipe at home

Overhead photo collage of how to make Oven Roasted Mushrooms step by step with the step direction written out on each photo.

FAQs: frequently asked questions

How should I prepare mushrooms and onions for roasting?

Before roasting, you’ll need to clean mushrooms with a damp cloth or damp paper towel to remove the dirt and trim the stems. You’ll also need to thaw the small onions if they’re frozen.

What temperature should I roast them at?

Roast onions with mushroom at 425°F (220°C). This higher temperature helps achieve a crisp exterior and rich caramelization.

How long should I roast mushrooms and onions together?

You’ll want to roast for a total of 20-30 minutes. Drizzle the mushrooms and onions with garlic butter sauce halfway through baking and toss to ensure even cooking and a buttery finish.

How can I add more flavor to the mushrooms and onions?

You’ll be tossing the onions and mushrooms in a garlic butter sauce infused with wine half way through roasting. This combination enhances the flavors and adds a rich, savory depth.

However, you can absolutely liven up the flavors even more by adding a variety of spices or other flavoring ingredients. Below are some ideas to inspire:

  • Fresh Herbs – basil, bay leaf, chives, cilantro, dill, tarragon, oregano (pictured), parsley, scallions and thyme (pictured).
  • Seasonings – cayenne, coriander, cumin or garlic
  • Vegetables – asparagus, bell peppers, fennel, leeks, potatoes, shallots or sun-dried tomatoes.
  • Cheese – grated parmesan, pecorino or shredded white cheddar cheese.
  • Other flavoring ingredients – bacon, bread crumbs, capers, lemon (pictured), marsala wine, sherry, soy sauce, wine or Worcestershire sauce.

How do I know when they are done?

The mushrooms with onions should be golden brown in color and tender in texture. Specifically, the small onions will be caramelized and the mushrooms will have a slightly crisp exterior with a tender interior.

Close-up photo of baked onions and mushrooms with garlic butter in a serving bowl.

Serving mushrooms with onions

This mushroom onion recipe is classically served as a side dish with steak, chicken, or pasta. However, they’re also terrific as a topping for toast, filling into omelettes, tossed into salads, and as a topping for pizza.

Common serving suggestions

  • With Steak: Roasted mushrooms and onions are a classic accompaniment to steaks. The rich flavors and textures complement the savory notes of the beef. If you’re looking for perfectly cooked steak recipes, be sure to try this recipe for Steak Slow Cooked in the Oven and Steak in the Slow Cooker.
  • As a Side Dish: Enjoy this mushroom onion recipe alongside grilled meats, roasted poultry, baked chicken meatballs, or crispy parmesan chicken cutlets. Their savory taste enhances any main course.
  • Over Pasta: Toss the garlic butter roasted mushrooms and onions with your favorite pasta, adding a splash of pasta water to create a deliciously rich and savory sauce. I love this roasted veggie side dish with Italian sausage pastas, lemon chicken pastas, and bolognese recipes.
  • On a Salad: Top a bed of mixed greens or spinach with the roasted vegetables. Add a sprinkle of parmesan cheese and a light vinaigrette for a hearty, flavorful salad.
  • With Rice or Quinoa: Serve the buttery onions with mushrooms over a bed of rice or quinoa for a nutritious and satisfying meal.

Unique Serving Suggestions

  • On a Pizza: Spread pizza sauce and then the roasted mushrooms and onions on a pizza crust before baking. Top with cheese and your other favorite pizza toppings for a gourmet twist on pizza night.
  • In a Wrap or Sandwich: Use the roasted vegetables as a filling for sandwiches and wraps wrap. Add some fresh greens, avocado, and a spread like avocado hummus or whipped ricotta cheese for a flavorful and satisfying meal.
  • As a Topping for Crostini: Spoon the roasted mushrooms and onions onto toasted crostini for an elegant appetizer or party snack. Garnish with a sprinkle of fresh herbs and a drizzle of balsamic reduction.
  • In an Omelette or Frittata: Incorporate the roasted mushrooms and onions into a fluffy omelette, rolled omelette, or spanish frittata for a hearty breakfast or brunch. The flavors blend beautifully with eggs and cheese.

Storing leftovers

Once mushrooms are oven baked, allow them to cool completely to room temperature. Then, transfer them to an airtight container or resealable bag. Store in the refrigerator for up to 3-5 days.

Freezing instructions

To freeze, allow cooked mushrooms and onions to cool completely. Next, transfer the veggies to a wax paper lined baking sheet in a single layer. Place the baking sheet in the freezer and flash freeze for 1-3 hours or until completely frozen. Transfer frozen mushrooms to a freezer-safe airtight container and store in the freezer for up to nine months.

When ready to use, remove the onions and mushrooms from the freezer, but do not thaw. Add frozen veggies directly to a dish or recipe that will be heated or cooked, such as soups, stews, casseroles or sauces. Alternatively, you can reheat the garlic butter mushroom and onions – see below for instructions.

Reheating instructions

Despite what a lot of critics say, you can safely reheat mushrooms – as long as they were properly stored!

If you placed your mushrooms in the freezer, you must thaw them overnight in the refrigerator before reheating.

To reheat oven cooked mushrooms, first melt a pat of butter in a skillet over medium-high heat. Then, add the mushrooms and sauté, stirring frequently. Cook the ‘shrooms until they are just warm throughout, about 3 minutes.

Close-up photo of roasted onions and mushrooms in garlic butter sauce.

Elevate your meals with this irresistible steakhouse style mushrooms and onions recipe that’s rich with caramelized flavors. Easy to prepare and impressively delicious, they’re perfect for pairing with steak, pasta, or as a standout side dish. Click below to print the full recipe and start creating your own delicious masterpiece today!

Until next week, friends, cheers!

Cheyanne

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More roasted veggie recipes!

Overhead photo of oven mushrooms with onions and garlic in a white serving bowl.

Mushrooms and Onions Recipe

5 from 3 votes
Author: Cheyanne Holzworth
Total Time: 25 minutes
Prep Time: 5 minutes
Cook Time: 20 minutes
Servings: 6 servings
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Discover the ultimate mushroom onion recipe with these perfectly roasted onions and mushrooms. This easy-to-make dish boasts a harmonious blend of caramelized onions and tender mushrooms in a rich garlic butter sauce, delivering an irresistible taste that perfectly enhances steak, pasta, chicken, and more! Best of all, you'll need just 5 minutes of hands on prep to make them.

Equipment

  • 1 Large Rimmed Baking Dish – for roasting mushroom with onion
  • 1 Large Liquid Measuring Cup – for making the garlic butter sauce

Ingredients 

  • 1 pound Mushrooms – cleaned and stems trimmed to be flush with the caps (Cremini or White Button)
  • 8 ounces Pearl Onions – defrosted if frozen (SEE NOTES)
  • 2 TBS Olive Oil – good quality
  • to taste Sea Salt & Ground Black Pepper
  • 5 TBS Unsalted Butter – cut into cubes
  • 1/3 Cup Dry White Wine – one you like to drink
  • 2-3 cloves Garlic – minced
  • 2 tsp EACH: Fresh Thyme and Fresh Oregano – chopped, plus more sprigs for roasting
  • Optional Garnishes: Fresh Parsley and Lemon Wedges

Instructions

  • Preheat Oven: Arrange oven rack to the middle position and then preheat the oven to 425 degrees F.
  • Season Mushrooms and Onions: Place the mushrooms and onions on a large, rimmed baking dish. Drizzle the oil evenly over the veggies and then season with a pinch of salt and pepper.
    Arrange the onions and mushrooms in a single, even spaced layer, with the mushrooms facing stem-side-down.
    Drop 4 sprigs of fresh thyme and 2 sprigs of rosemary on top of the mushrooms and onions.
  • Partially roast: Place mushrooms and onions in the oven. Roast for 15 minutes or until lightly browned.
  • Meanwhile, Make the Butter Sauce: In a large, microwave-safe liquid measuring cup, combine the butter with the wine, garlic, thyme and oregano. Season with ¼ teaspoon salt and 1/8 teaspoon pepper.
    Microwave at 50% power for 1 minute. Stir the butter sauce and return to the microwave. Heat again on 50% power for 1 1/2 minutes in 30 second increments. (SEE NOTES)
  • Toss Onions and Mushrooms with Butter Sauce: Remove the mushrooms and onions from the oven. Then drizzle the butter sauce evenly over the veggies and gently toss or stir to coat them in the butter.
  • Finish Roasting: Return the onions and mushrooms to the oven and continue roasting for 5-10 minutes, or until mushrooms are browned and tender.
    Taste the veggies and adjust for seasoning with salt and pepper.
  • Serve Mushrooms with Onions: Transfer mushrooms and onions to a serving dish. Then, drizzle any remaining butter sauce in the baking dish all over the mushrooms and onions.
    Garnish with fresh herbs and lemon, if using. Enjoy immediately!
    Overhead photo of oven mushrooms with onions and garlic in a white serving bowl.

Notes

  1. Mushrooms: You can use whatever variety of mushrooms you love, just make sure you pick ones that are roughly the same size for even cooking. If using larger mushrooms, I recommend halving or quartering them.
  2. Onions: If you can’t find pearl onions or simple don’t like them, feel free to substitute 8 ounces of halved or quartered shallots instead! Alternatively, you can omit the onions completely and use an extra 8 ounces of mushrooms.
  3. When making the butter sauce in the microwave, be very careful! The wine and butter mixture will bubble up when it is heating, so make sure you are using a large measuring cup and microwave in short increments. I recommend at least a 2 cup liquid measuring cup.  Alternatively, you can melt the butter with wine, garlic and seasonings on the stove-top instead – just do it over low to medium-low heat.
  4. Need to Scale the Recipe? Hover your mouse over the number of servings in the recipe card. You’ll see a sliding scale pop up, you can use that to scale the recipe up or down as needed.
  5. Got questions? I’ve got answers! If you ever run into an issue, have a question, or need any clarification – please feel free to drop them in the comments section. I’m happy to help when I can! 
     
Nutritional information is provided as a courtesy and the nutrition facts are an estimate based upon 6 servings. Exact information will depend upon the brands of ingredients and precise measurements used.

Nutrition

Calories: 169kcal    Carbohydrates: 7g    Protein: 3g    Fat: 14g    Saturated Fat: 7g    Polyunsaturated Fat: 1g    Monounsaturated Fat: 6g    Trans Fat: 0.4g    Cholesterol: 25mg    Sodium: 8mg    Potassium: 312mg    Fiber: 1g    Sugar: 3g    Vitamin A: 292IU    Vitamin C: 5mg    Calcium: 17mg    Iron: 1mg
Course: Side Dish
Cuisine: American

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