Caramelized Onion & Gruyère Stuffed Mushrooms Recipe

Introduction

These Caramelized Onion & Gruyère Stuffed Mushrooms make a perfect appetizer or savory snack. The rich sweetness of slowly caramelized onions pairs beautifully with the nutty flavor of Gruyère cheese, all nestled inside tender mushroom caps.

Ingredients

• 12 large button or cremini mushrooms
• 2 teaspoons olive oil
• Salt and freshly ground black pepper, to taste
• 2 medium yellow onions, thinly sliced
• 3 tablespoons unsalted butter
• 1 tablespoon fresh thyme leaves
• ¼ cup dry white wine (optional)
• 1 cup grated Gruyère cheese
• ¼ cup panko breadcrumbs
• 1 large egg, lightly beaten

Instructions

1. Step 1: Gently wipe each mushroom with a damp paper towel to remove dirt. Using a small spoon, carefully twist and remove stems to create a cavity, keeping caps intact. Toss caps with olive oil, season with salt and pepper, and place stem side up on a parchment-lined baking sheet.
2. Step 2: Heat a large skillet over medium-low heat and melt butter. Add thinly sliced onions and a pinch of salt, stirring to coat. Cook slowly for 25–30 minutes, stirring every few minutes, until onions turn deep amber and jam-like in consistency.
3. Step 3: Sprinkle fresh thyme over the caramelized onions and stir for 30 seconds. If using, add white wine to deglaze the pan, scraping up browned bits, and let the liquid reduce by half, about 2 minutes.
4. Step 4: Transfer the onion mixture to a bowl. Fold in grated Gruyère, panko breadcrumbs, and beaten egg until evenly combined. Taste and adjust seasoning with salt, pepper, or extra thyme if desired.
5. Step 5: Spoon the filling generously into each mushroom cap. Bake at 375°F (190°C) for about 20 minutes or until the tops are golden and the mushrooms are tender. Serve warm.

Tips & Variations

• For a vegetarian option, use a plant-based egg substitute or increase the panko for binding.
• Swap Gruyère with a sharp white cheddar or fontina for a different flavor profile.
• Adding a small pinch of smoked paprika to the filling can introduce a subtle smoky depth.

Storage

Store leftover stuffed mushrooms in an airtight container in the refrigerator for up to 3 days. Reheat gently in a low oven or microwave until warm, being careful not to overcook and dry them out.

How to Serve

Serve this delicious recipe with your favorite sides.

FAQs

Can I prepare the filling ahead of time?

Yes, you can make the caramelized onion filling a day in advance and refrigerate it. Assemble and bake the mushrooms just before serving for best results.

What type of mushrooms work best for this recipe?

Large button or cremini mushrooms are ideal because their size provides a good cavity to hold the filling, and they have a mild flavor that complements the rich filling nicely.