Ingredients
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
Preparation
Step 1Preheat oven to 450°. Line a rimmed baking sheet with parchment paper.Step 2In 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.Step 3Increase 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.Step 4Place 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.)Step 5Top mushrooms with onion mixture and Gruyère. Switch oven to broil and broil stuffed mushrooms until cheese is bubbly and melty, about 2 minutes.Step 6Sprinkle with parsley before serving.
