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Rich meaty portobello mushroom caps stuffed with slow-roasted onions topped with gruyere cheese and toasted breadcrumbs. Pair with a side salad for a simple but luxurious meatless date-night meal.

2 servings

French Onion Stuffed Portobellos

15 minPrep Time

55 minCook Time

1 hr, 10 Total Time

Save RecipeSave Recipe
Recipe Image


  • 4 yellow onions, cut into ¼ inch rings
  • 4 tbsp olive oil, divided
  • 2 tbsp balsamic vinegar
  • 2 tsp kosher salt, divided
  • 1 tsp brown sugar
  • 3-4 sprigs of fresh thyme
  • 2 bay leaves
  • 4 Portobello Caps
  • 125g (4.5oz) Gruyere, shredded
  • 1 tbsp salted butter
  • ½ cup panko breadcrumbs


  1. Preheat the oven to 350°F.
  2. Place the onions in a large bowl. Add 2 tablespoons of the olive oil, balsamic vinegar, 1 teaspoon of kosher salt, and brown sugar. Using your hands, toss the onions to ensure they are evenly coated.
  3. Place the onions in a large casserole dish and add the thyme and bay leaves. Cover with tin foil and place the onions in the oven. Let roast for 25 minutes.
  4. While the onions are roasting, place the mushrooms cup-side-up on a baking sheet lined with parchment paper. Drizzle the remaining olive oil over the mushrooms and sprinkle them with the remaining salt.
  5. When the 25 minutes have passed, remove the tin foil and add the mushrooms to the oven. Roast for an additional 25 minutes.
  6. While the veggies are roasting, melt the butter in a skillet over medium heat. Once the butter is foamy, add the breadcrumbs and toast, shaking the pan frequently, until the crumbs are golden. Take the pan off of the heat and set it aside.
  7. Take the mushrooms and onions out of the oven. Pack as many of the onions on top of the portobello mushroom caps as possible and cover them with the gruyere. Place the mushrooms under the broiler. Cook until the cheese is bubbly. Keep an eye on it.
  8. Take the mushrooms out of the oven and sprinkle with the breadcrumbs. Garnish with a fresh sprig of thyme and serve immediately.

Recipe by Susan


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