Description
This delicious French Onion Mushroom Casserole combines caramelized onions and tender mushrooms in a creamy, cheesy sauce topped with a crunchy breadcrumb crust. Perfect as a hearty side dish or a comforting vegetarian main, it offers rich flavors with Gruyère, Parmesan, and a touch of thyme for depth. Baked to golden perfection, this casserole is an easy and crowd-pleasing recipe ideal for family dinners or special occasions.
Ingredients
Scale
Main Ingredients
- 2 tablespoons butter
- 2 large yellow onions, thinly sliced
- 1 tablespoon olive oil
- 4 cups mushrooms, sliced (button, cremini, or a mix)
- 3 cloves garlic, minced
- 1 teaspoon dried thyme
- ½ teaspoon ground black pepper
- 1 cup vegetable broth (or chicken broth)
- ½ cup heavy cream
- 1 cup shredded Gruyère cheese (or Swiss cheese)
- ½ cup shredded Parmesan cheese
- 1 tablespoon fresh parsley, chopped (optional, for garnish)
Topping
- 1 cup breadcrumbs (preferably panko for extra crunch)
- 2 tablespoons melted butter
- ¼ cup grated Parmesan cheese
Instructions
- Caramelize the Onions: In a large skillet, melt the butter over medium heat. Add the sliced onions and cook, stirring occasionally, for 15-20 minutes, or until the onions are golden brown and caramelized. If the onions start to burn, add a splash of water and continue to cook until they soften and caramelize.
- Cook the Mushrooms: Add the olive oil to the skillet with the onions. Add the sliced mushrooms and cook, stirring occasionally, for 7-8 minutes until the mushrooms release their moisture and become tender.
- Add Seasonings: Add the garlic, thyme, and black pepper to the skillet, cooking for another minute until the garlic becomes fragrant.
- Make the Sauce: Pour in the vegetable broth and let it simmer for 2-3 minutes, allowing the flavors to meld together.
- Thicken the Sauce: Stir in the heavy cream and bring the mixture to a simmer. Let it cook for another 3-4 minutes until the sauce thickens slightly.
- Preheat Oven: Preheat your oven to 375°F (190°C) to prepare for baking the casserole.
- Assemble the Casserole: Transfer the onion and mushroom mixture to a greased 9×13-inch baking dish.
- Add Cheese: Sprinkle the shredded Gruyère and Parmesan cheese over the mixture, stirring gently to combine the cheeses evenly.
- Prepare the Topping: In a small bowl, mix the breadcrumbs with melted butter and grated Parmesan until the breadcrumbs are well coated.
- Add Topping: Evenly sprinkle the breadcrumb mixture over the top of the casserole.
- Bake the Casserole: Place the casserole in the preheated oven and bake for 20-25 minutes, or until the top is golden brown and the casserole is bubbling.
- Rest and Serve: Remove the casserole from the oven and let it sit for a few minutes before serving.
- Garnish and Enjoy: Optionally garnish with chopped fresh parsley and serve the casserole hot.
Notes
- For best texture, use a mix of button and cremini mushrooms, or your favorite mushrooms.
- Gruyère cheese can be substituted with Swiss cheese if preferred.
- If you want a richer flavor, use chicken broth instead of vegetable broth.
- To make the casserole gluten-free, substitute breadcrumbs with gluten-free breadcrumbs.
- The casserole can be prepared a day ahead and baked fresh before serving.
- Store leftovers covered in the refrigerator for up to 3 days.
- Reheat in the oven to retain the crunchy topping rather than microwave.
- Prep Time: 15 minutes
- Cook Time: 40 minutes
- Category: Casserole
- Method: Baking
- Cuisine: French
