Stuffed mushrooms may not seem like the most exciting party appetizer. But cheesy French onion stuffed mushrooms are an entirely different story.
- 2 tbsp. butter
- 1 tbsp. extra-virgin olive oil
- 2 large yellow onions, halved and thinly sliced
- Kosher salt
- Freshly ground black pepper
- 2 tsp. fresh thyme leaves
- 2 cloves garlic, minced
- 1/4 c. dry sherry
- 1 lb. baby bella mushrooms, stems removed
- 1 c. shredded Gruyère
- 2 tsp. freshly chopped parsley
Preheat oven to 450°. Line a rimmed baking sheet with parchment paper.
In a large skillet over medium heat, heat butter and oil. Add onions and season with salt, pepper, and thyme. Reduce heat to medium-low and cook, stirring occasionally, until onions are caramelized and jammy, about 20 minutes.
Increase heat to medium-high, stir in garlic and cook, stirring, until fragrant, about 30 seconds. Stir in sherry and simmer until almost completely reduced, 2 minutes. Remove from heat.
Place mushrooms stem-side up on the prepared baking sheet. Roast mushrooms on top rack until softened, about 10 minutes. Remove from oven. (If any moisture gathers in mushroom caps, blot moisture with a paper towel.)
Top mushrooms with onion mixture and cheese. Switch oven to broil and broil stuffed mushrooms until cheese is bubbly and melty, about 2 minutes.
Sprinkle with parsley before serving.