Cook Bacon: Add bacon to a COLD cast iron skillet (or nonstick skillet) and place skillet over medium heat. Cook bacon until crispy and fat has rendered, about 11-15 minutes. Use a slotted spoon to remove bacon to paper towel lined plate and set aside. Pour all but one tablespoon of bacon fat into a small container and set aside.
Add onion to bacon drippings in the pan season with ¼ teaspoon salt and 1/8 teaspoon pepper. Cook, stirring occasionally, until the onion is soft and translucent, about 5-8 minutes. Use a slotted spoon (reserving bacon grease) to transfer the onion to a medium sized mixing bowl. Add in the drained bacon. Allow to cool.
Meanwhile: Remove moisture from spinach by placing it in a large tea towel, kitchen towel, or paper towels and squeeze until spinach is mostly dry. Add to the bowl of onion and bacon along with the goat cheese, cream, nutmeg and 1/8 teaspoon of the pepper. Stir to combine. Set aside in the refrigerator.
Cook the Mushrooms: Heat the cast iron skillet, with reserved bacon grease, over medium heat. (You want about 2 tablespoons of bacon grease in the skillet. If the skillet looks dry, add extra virgin olive oil). Add half of the mushrooms and season with ¼ teaspoon salt and 1/8 teaspoon pepper. Cook, flipping once, until tender and golden brown, about 2-3 minutes per side. Transfer to a paper towel lined plate, cavity side facing down. Add 2 tablespoons of olive oil to the pan and repeat with remaining mushrooms, salt and pepper.
Preheat oven to 350 degrees. Line a sheet pan with aluminum foil for easy clean up. Spray with non-stick cooking spray.
Assemble and Bake Mushrooms: Transfer drained mushrooms, cavity side up, to the prepared baking sheet. Place 1 heaping teaspoon of the spinach/bacon filling in the cavity of each mushroom. Top with parmesan cheese and panko. Bake until stuffed mushrooms are warmed, 5-7 minutes. Serve and enjoy!
Notes
*Yield: about 36 stuffed mushrooms *Look for Mushrooms that are uniform in size and slightly larger than bite size, as they will shrink when cooked. *Spinach and bacon filling can be prepared up to 2 days in advance and stored, covered, in the refrigerator. Prepare stuffed mushrooms as directed. *Recipe adapted from “Cocktail Food” by Barber, Whiteford and Narlock.