Caramelized Onion and Gruyère Stuffed Portobello Mushrooms
Hearty mushrooms stuffed with slow-simmered onions and melted Gruyère, baked until golden and bubbling. This mediterranean-inspired vegetarian (gluten-free) ready in about 45 minutes pairs large portobello mushrooms, medium yellow onions, grated Gruyère cheese for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 180 calories and feeds 4, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.
Ingredients
- 4 large portobello mushrooms
- 2 medium yellow onions
- 1/2 cup grated Gruyère cheese
- 1 tbsp balsamic vinegar
- 2 tbsp olive oil
- 1 tsp chopped fresh thyme
- 1/4 tsp salt
Instructions
- Step 1: Preheat oven to 375°F (190°C). Remove stems from mushrooms and scrape out gills with a spoon; brush mushroom caps with 1 tbsp olive oil.
- Step 2: Thinly slice onions and cook in remaining 1 tbsp olive oil over medium-low heat with 1/4 tsp salt; stir occasionally for 25-30 minutes until deeply golden and caramelized.
- Step 3: Stir in balsamic vinegar and thyme into onions, then remove from heat and let cool slightly.
- Step 4: Mix caramelized onions with half the grated Gruyère, then spoon mixture into mushroom caps until filled.
- Step 5: Top with remaining Gruyère, place on a baking sheet, and bake for 15-18 minutes until cheese is bubbly and golden.
Equipment for this recipe
Top-rated tools to make this recipe successfully.
Frequently asked questions
How long does Caramelized Onion and Gruyère Stuffed Portobello Mushrooms take to make?
Total time is about 45 minutes (25 min prep + 20 min cook). Most home cooks find this fits comfortably into a weeknight; double the batch on Sunday for two dinners.
How do I store leftover Caramelized Onion and Gruyère Stuffed Portobello Mushrooms?
Cool to room temperature within 2 hours, then store in an airtight container in the fridge for up to 4 days. Reheat covered in a 350°F oven for 10-12 minutes, or microwave at 70% power in 60-second bursts to keep large portobello mushrooms from drying out.
Can I substitute ingredients in Caramelized Onion and Gruyère Stuffed Portobello Mushrooms?
Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.
How do I scale Caramelized Onion and Gruyère Stuffed Portobello Mushrooms for a different number of people?
The recipe is written for 4 servings. Multiply each ingredient by (your serving target / 4). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.
Is Caramelized Onion and Gruyère Stuffed Portobello Mushrooms gluten-free?
Yes — this recipe is tagged gluten-free based on its ingredient list. Always cross-check labels for packaged ingredients (sauces, broths, condiments) since formulations vary by brand.
What others are saying
- ★★★★★
The flavors in this caramelized are incredible.
- ★★★★★
Best recipe I've made this month.
- ★★★★☆
Enjoyable meal. Instructions could be a touch more detailed on the timing.
