5 from 5 votes
Overhead, landscape photo of Brussels Sprouts au Gratin garnished with fresh thyme with two spoons, a ramekin of grated cheese and a neutral colored napkin next to the dish.
Brussels Sprouts Gratin
Prep Time
15 mins
Cook Time
40 mins
Total Time
55 mins

This Creamy Roasted Brussels Sprouts and Pearl Onion Gratin is the perfect holiday side dish! The brussels sprouts and onions are coated in a decadent, cheesy bechamel sauce and topped with a parmesan, pinenut and panko crumb topping. This side is indulgent, delicious and sure to please!

Course: Side Dish
Cuisine: American, French, Fusion
Servings: 6
Calories: 273 kcal
  • 1 Pound Brussels Sprouts – trimmed, outer leaves removed & cut in half or quartered (SEE NOTE)
  • 8 ounces Pearl Onions – peeled & trimmed (SEE NOTES)
  • Olive Oil Non-stick Spray
  • Kosher Salt & Ground Black Pepper - to taste
  • 2 ½ TBS Unsalted Butter - DIVIDED
  • 1 ½ TBS All Purpose Flour
  • 1 ½ Cups Half and Half or Heavy Cream
  • 4 sprigs fresh Thyme - plus more for garnish
  • Pinch Nutmeg
  • 4 Ounces Grated Gruyere Cheese - DIVIDED
  • 2/3 Cup Panko Bread Crumbs (can substitute fresh bread crumbs)
  • ¼ Cup Pine Nuts – roughly chopped
  • 1 Clove Garlic - minced
  1. Preheat Oven:  Preheat oven to 400 degrees F.  Spray a 2 quart gratin or baking dish with non-stick cooking spray.  Set aside.Preheat Oven:

  2. Par-bake Vegetables:  Line a large, rimmed baking sheet with aluminum foil for easy clean up.  Add brussels sprouts and onions.  Spray vegetables with non-stick cooking spray.  Season generously with salt and pepper.  Toss to coat.  Spread vegetables out in an even layer.  Bake for 15-20 minutes, tossing halfway through cooking, or until vegetables are almost fork tender.  Remove from oven and transfer to prepared baking dish.

  3. While the vegetables are baking, make the sauce:  In a medium-size saucepan, melt 1 ½ tablespoons of butter over medium heat.  Add the flour and whisk continuously for 1-2 minutes or until the mixture is blonde in color.  Add in the half-and-half.  Increase heat to medium-high and bring to a boil.  Immediately reduce heat to medium-low to maintain a gentle simmer.  Add sprigs of thyme and nutmeg.  Season generously with salt and pepper.  Cook, stirring occasionally, for 10 minutes or until sauce is thickened.  Remove sprigs of thyme with tongs and discard.  Turn off heat and add in 3 ounces (heaping ¾ cup) of the cheese.  Stir until the cheese is fully incorporated.  Remove from heat. Taste and adjust for seasoning with salt and pepper. 

  4. While the sauce is cooking, prepare the topping:  Melt 1 tablespoon of butter.  Add it to a small mixing bowl.  Add in the panko, pine nuts, garlic, and 1 ounce (about ¼ cup) of gruyere cheese.  Season with salt and pepper.  Stir well to combine.  Set aside.

  5. Prepare the gratin:  Pour the sauce evenly over the brussels sprouts and onions in the prepared baking dish.  Sprinkle the breadcrumb topping evenly over top. 

  6. Bake:  Bake gratin UNCOVERED, for 18-22 minutes or until the sauce is bubbling and the top is golden brown.  If the top starts to brown too quickly towards the end of baking, lightly tent the dish with aluminum foil. 

  7. Rest and Serve:  Allow to rest for 5-10 minutes before serving.  Garnish with thyme and Enjoy!

Recipe Notes
  1. You want the brussels sprouts to be uniform in size. If the brussels sprouts are huge, quarter them.  If they are on the medium or small side, half them.  You want them to be roughly the same size as the onions. 

  2. You can use frozen pearl onions for ease and convenience!  Thaw the onions and pat dry before proceeding with recipe.

  3. You can easily add bacon if desired!  Add cooked, crumbled bacon to par-roasted brussels sprouts and onions before pouring on the cheese sauce and topping with breadcrumbs.  

  4. The gratin can be assembled a day in advance through step 5 - DO NOT SPRINKLE WITH TOPPING.  Cover the dish with plastic wrap and refrigerated overnight. Allow the gratin to sit at room temperature for 30 minutes before sprinkling with breadcrumb topping and baking.
Nutrition Facts
Brussels Sprouts Gratin
Amount Per Serving
Calories 273 Calories from Fat 171
% Daily Value*
Fat 19g29%
Saturated Fat 9g56%
Cholesterol 40mg13%
Sodium 129mg6%
Potassium 480mg14%
Carbohydrates 20g7%
Fiber 4g17%
Sugar 4g4%
Protein 6g12%
Vitamin A 1025IU21%
Vitamin C 69.1mg84%
Calcium 122mg12%
Iron 2mg11%
* Percent Daily Values are based on a 2000 calorie diet.