French Onion Stuffed Mushrooms turn everyone’s favorite soup into a decadent bite sized appetizer. Stuffed with caramelized onions and layers of melty Gruyère, and crisp panko topping for the perfect irresistible bite.
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About This Recipe
These French onion stuffed mushrooms take all the flavors of the classic soup and transform them into a decadent bite-sized appetizer.
Sweet, jammy caramelized onions are tucked into tender mushroom caps, topped with nutty Gruyère cheese and finished with a crispy Parmesan-panko topping. Every bite is savory, creamy, and crunchy with just the right balance of richness from the cheese and sweetness from the onions, while the marsala wine cuts through beautifully.
These make a show-stopping addition to any holiday spread. If you already love my boursin stuffed mushrooms, this recipe takes things to the next level with bold, French-inspired flavors.
📋 Ingredients
- Baby portobello mushrooms (cremini) – Look for medium-sized mushrooms that are large enough to hold the filling. I prefer wiping mushrooms with a damp paper towel instead of rinsing to avoid excess water.
- Yellow onions – Take the time to caramelize them slowly. Dicing the onions helps the filling fit neatly inside each mushroom cap.
- Olive oil and butter – The combination adds richness and helps with even browning.
- Fresh thyme – Classic herb pairing with mushrooms and cheese. If fresh isn’t available, use ½ to ¾ teaspoon dried thyme.
- Marsala wine – Adds sweetness and depth. You can substitute with sherry, cognac, or red wine.
- Gruyère cheese – Nutty, melty, and perfect for French onion flavors. Keep it cold before grating to make shredding easier.
- Panko breadcrumbs – Crisp and light; they toast beautifully. Gluten-free panko also works.
See recipe card for full information on ingredients and quantities.
🍋 Substitutions and Variations
- Mushrooms – Use baby bella (cremini) or white button mushrooms. For a larger appetizer, use portobello caps.
- Cheese – If Gruyère isn’t available, substitute with a good-quality Swiss cheese. Gouda will also work for a creamier, milder flavor.
- Breadcrumbs – Swap with regular breadcrumbs if you prefer, but panko gives the best crunch. Gluten-free panko works well too.
- Wine – Marsala is classic, but sherry, cognac, or a dry red wine also pair beautifully. White wine such as Chardonnay can be used for a lighter flavor.
- Herbs – Fresh thyme is traditional, but parsley, tarragon, or chives would all be delicious variations.
⏲️ Instructions
Caramelizing the Onions
Start pale – Onions soften and turn light yellow after 10–15 minutes.
Golden stage – At 30 minutes, they deepen in color and shrink down.
Getting jammy – Around 40 minutes, browning starts to develop.
Fully caramelized – By 50–55 minutes, they’re dark amber and sweet.
Make the Stuffed Mushrooms
Cleaned mushroom caps – Stems removed, ready for par-baking.
Drain liquid – After par-baking, pour out any excess moisture.
Stuff the mushrooms – Add caramelized onion mixture into each mushroom.
Final bake – Top with Gruyère and herbed panko, then bake until golden and bubbly.
📍 Recipe Tips
- Clean mushrooms gently – Wipe with a damp cloth or paper towel instead of rinsing to prevent sogginess.
- Pre-bake the mushrooms – Par-baking helps release liquid so the final dish isn’t watery. Drain after baking.
- Caramelize the onions slowly – Don’t rush this step! Cooking low and slow (45–50 minutes) develops the deep golden color and sweet flavor. Covering the pan with a lid helps trap moisture and prevent burning.
- Dice onions for easier stuffing – Diced onions fit better into the mushroom caps than sliced onions.
- Toast the breadcrumbs with oil – Tossing panko with olive oil keeps them from burning and ensures a golden crunch.
- Make ahead – You can stuff the mushrooms (without topping) up to 2 days in advance. Before serving, add the Gruyère, breadcrumb mixture, and bake until melted.
Serving Suggestions
These French onion stuffed mushrooms shine on any appetizer spread:
- Pair with a simple charcuterie board.
- Serve alongside goat cheese–stuffed phyllo cups.
- Add to a platter with steak crostini.
- Include in a holiday menu with roast Cornish hens.
- Make them a French-inspired starter before chicken Provençal, coq au vin, or beef bourguignon.
More Mushroom Recipes to Try
Love this recipe? Please leave a 5-star 🌟🌟🌟🌟🌟rating in the recipe card below & a review in the comments section further down the page.
French Onion Stuffed Mushrooms
LittleFerraroKitchen.com
Ingredients
- 1 pint baby portobello mushrooms about 12–14 medium mushrooms
- 2 medium yellow onions diced
- 2 tablespoons unsalted butter
- 3 tablespoons olive oil divided, plus more as needed
- 2 garlic cloves minced
- 4 sprigs fresh thyme leaves removed (plus extra for garnish)
- Salt and freshly ground black pepper to taste
- 2 tablespoons marsala wine or sherry, cognac, or red wine
- ½ cup shredded Gruyère cheese
- ¼ cup panko breadcrumbs
- 2 tablespoons grated Parmesan cheese
Instructions
- Preheat the oven to 350 degrees Fahrenheit. Line a baking sheet with parchment paper.
- Prep the mushrooms: Remove stems, finely chop them, and set aside. Place mushroom caps on the baking sheet, stem side up, drizzle lightly with olive oil, and season with salt and pepper. Bake for 10 minutes. Drain off any liquid and set aside to cool slightly.
- Caramelize the onions: In a large skillet, heat butter and 1 tablespoon olive oil over medium heat. Add the diced onions, season lightly with salt, and cook slowly for 45 to 50 minutes, stirring occasionally. Keep the skillet covered for part of the cooking time to trap moisture. The onions should become deeply golden and jammy.
- Add stems and aromatics: Stir in the chopped mushroom stems and cook for 2 minutes until softened. Add the garlic, thyme and saute for another 30 seconds to 1 minute.
- Deglaze: Carefully pour in the marsala wine and cook until most of the liquid has evaporated and the mixture is rich and concentrated. Taste and adjust seasoning and remove from heat.
- Make the breadcrumb topping: In a small bowl, combine the panko breadcrumbs, Parmesan and parsley. Drizzle with 1 to 2 tablespoons olive oil and toss until lightly coated.
- Assemble the mushrooms: Spoon the onion mixture into each mushroom cap. Sprinkle with shredded Gruyère, then top with the breadcrumb-Parmesan mixture.
- Bake: Return the mushrooms to the oven and bake for 10-12 minutes, until the cheese is melted and the breadcrumbs are golden. For extra crispness, broil for 1 minute at the end, watching closely.
- Serve: Garnish with fresh thyme leaves and an extra sprinkle of Parmesan. Serve warm.
Notes
- Clean mushrooms – Wipe with a damp cloth, not water.
- Par-bake the mushrooms – Helps release liquid; drain before stuffing.
- Slow-cook onions – Caramelize 45–50 minutes for best flavor.
- Dice onions – Fits better in mushroom caps.
- Toast panko – Toss with olive oil for golden crunch.
- Make ahead – Stuff up to 2 days early; add cheese/topping before baking.
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