French Onion Mushroom Casserole
French Onion Mushroom Casserole is a comforting, savory dish that brings together the rich flavors of caramelized onions, earthy mushrooms, and a creamy, cheesy sauce, all topped with a crispy, golden breadcrumb crust. This casserole combines the best of two beloved classics—French onion soup and mushroom dishes—into one irresistible, hearty side or vegetarian main course. Perfect for cozy dinners, holiday feasts, or anytime you’re craving a flavorful, indulgent treat, this casserole is sure to become a favorite in your recipe rotation!
Ingredients:
1 tablespoon olive oil
2 tablespoons butter
1 medium onion, thinly sliced
2 cups mushrooms, sliced (preferably a mix of cremini and white mushrooms)
3 cloves garlic, minced
1 teaspoon dried thyme (or 2 teaspoons fresh thyme)
Salt and pepper to taste
1 cup vegetable or chicken broth
1/2 cup heavy cream
1/2 cup grated Gruyère cheese (or Swiss cheese)
1/4 cup grated Parmesan cheese
1/2 cup breadcrumbs (panko or regular)
1 tablespoon fresh parsley, chopped (for garnish)
Instructions:
Preheat the oven to 375°F (190°C). Grease a 9×9-inch baking dish with a little butter or cooking spray.
Cook the onions:
In a large skillet, heat the olive oil and butter over medium heat.
Add the sliced onions, and cook for about 15-20 minutes, stirring occasionally until they become golden brown and caramelized.
Cook the mushrooms:
Add the sliced mushrooms and minced garlic to the skillet with the onions.
Stir in the thyme, salt, and pepper, and cook for another 8-10 minutes until the mushrooms release their moisture and soften.
Prepare the sauce:
Once the mushrooms have softened, pour in the vegetable or chicken broth and bring it to a simmer.
Add the heavy cream, and let the mixture simmer for about 5 minutes to thicken slightly. Taste and adjust the seasoning as needed.
Combine everything:
Pour the mushroom and onion mixture into the prepared baking dish.
Sprinkle the Gruyère and Parmesan cheeses over the top.
Make the topping:
In a small bowl, combine the breadcrumbs with a tablespoon of melted butter (this helps the breadcrumbs brown nicely).
Sprinkle the breadcrumbs evenly over the casserole.
Bake:
Place the casserole in the oven and bake for 20-25 minutes, or until the cheese is bubbly and the breadcrumb topping is golden and crispy.
Garnish and serve:
Remove the casserole from the oven, and sprinkle fresh parsley on top for a burst of color and flavor.
Serve hot, and enjoy!
Tips:
For extra flavor, you can add a splash of white wine to the onions and mushrooms while they cook.
You can make this dish ahead of time and refrigerate it. Just bake it right before serving.
For a vegan version, substitute the heavy cream with coconut cream and use vegan cheese options.