Description
This French Onion Mushroom Casserole is a creamy, cheesy, and comforting side dish perfect for holidays or weeknight dinners. Featuring caramelized onions, sautéed mushrooms, and a rich blend of Gruyère and mozzarella cheeses, it’s topped with buttery crushed crackers for a delightful crunch. This vegetarian casserole can also serve as a hearty main when paired with grains like wild rice or quinoa.
Ingredients
Scale
For the Casserole:
- 2 tablespoons unsalted butter
- 1 tablespoon olive oil
- 2 large onions, thinly sliced
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper
- 1 teaspoon sugar
- 3 cloves garlic, minced
- 1 pound cremini or button mushrooms, sliced
- 1/2 teaspoon dried thyme
- 1 tablespoon Worcestershire sauce
- 1/2 cup sour cream
- 1/4 cup mayonnaise
- 1/2 cup shredded Gruyère or Swiss cheese
- 1/2 cup shredded mozzarella cheese
For the Topping:
- 1 cup crushed buttery crackers (like Ritz)
- 1 tablespoon melted butter
- chopped parsley for garnish (optional)
Instructions
- Preheat and Prepare: Preheat your oven to 375°F (190°C) and grease a medium casserole dish to prevent sticking.
- Caramelize Onions: In a large skillet, melt the butter and olive oil over medium heat. Add the thinly sliced onions, salt, pepper, and sugar. Cook for 15–20 minutes, stirring occasionally, until the onions become soft and develop a deep golden color, indicating they are perfectly caramelized.
- Sauté Mushrooms and Garlic: Add the minced garlic and sliced mushrooms to the skillet with the caramelized onions. Continue cooking for another 8–10 minutes until the mushrooms are browned and most of their moisture has evaporated. Stir in the dried thyme and Worcestershire sauce, then remove the skillet from heat.
- Mix the Creamy Base: In a large bowl, combine the sour cream, mayonnaise, shredded Gruyère (or Swiss), and shredded mozzarella cheeses. Stir until blended smoothly.
- Combine Mixture: Add the cooked onion and mushroom mixture to the creamy base and stir everything together until thoroughly combined.
- Assemble the Casserole: Transfer the mixture into the greased casserole dish, spreading it evenly. In a small bowl, mix the crushed buttery crackers with the melted butter, then sprinkle this topping evenly over the casserole.
- Bake: Place the casserole dish in the oven and bake for 20–25 minutes, or until the topping is golden brown and bubbly.
- Garnish and Serve: Remove from the oven, garnish with chopped parsley if desired, and serve warm for a comforting and delicious meal or side dish.
Notes
- This casserole makes a great holiday side dish or a satisfying vegetarian main course.
- For a heartier meal, add cooked wild rice or quinoa to the mixture before baking.
- Leftovers can be stored in the refrigerator and reheated the next day without losing flavor.
- Prep Time: 20 minutes
- Cook Time: 25 minutes
- Category: Side Dish
- Method: Baking, Sautéing
- Cuisine: American
Nutrition
- Serving Size: 1 scoop (about 1/6 of casserole)
- Calories: 320
- Sugar: 6g
- Sodium: 420mg
- Fat: 24g
- Saturated Fat: 10g
- Unsaturated Fat: 12g
- Trans Fat: 0g
- Carbohydrates: 18g
- Fiber: 2g
- Protein: 7g
- Cholesterol: 45mg
