Craving comfort food with a sophisticated twist? This French Onion Mushroom Casserole combines the deep, rich flavors of French onion soup with tender mushrooms, caramelized onions, and melted Swiss cheese, all topped with crispy, garlicky baguette slices. It’s the ultimate casserole for a cozy dinner, a side dish for gatherings, or a hearty meal to enjoy with loved ones. With layers of flavor and a golden cheesy topping, this recipe is sure to impress and satisfy.
Ingredients
- Olive oil for the pan
- 1¾ pounds pearl onions (click here for how to peel pearl onions)
- 8 ounces Crimini mushrooms, washed, dried, and thinly sliced
- 1½ tablespoons thyme, finely chopped
- 2 cups beef broth
- ½ cup dry red wine
- 5 tablespoons unsalted butter, softened, divided
- 2 tablespoons all-purpose flour
- 1 (approximately 2-foot) skinny French baguette, thinly sliced
- 1½ tablespoons garlic, minced, divided
- 1½ cups Swiss cheese, grated, divided
- Sea salt and freshly ground black pepper, to taste
Instructions
- Prepare the Onions and Mushrooms : Heat a drizzle of olive oil in a large skillet over medium heat. Add the pearl onions and cook for about 5–7 minutes, stirring occasionally, until they are golden and caramelized. Season with a pinch of salt and transfer to a plate. In the same skillet, add a bit more olive oil and the sliced Crimini mushrooms. Cook for 5–7 minutes, or until the mushrooms release their moisture and are browned. Add the thyme and stir for 1 minute.
- Make the Sauce : In the skillet with the mushrooms, pour in the beef broth and red wine. Bring to a simmer and let it reduce slightly for 5–6 minutes. In a small saucepan, melt 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1–2 minutes to form a roux. Slowly whisk the roux into the mushroom sauce until it thickens. Add the caramelized pearl onions back into the skillet and mix well. Season with salt and freshly ground black pepper to taste.
- Prepare the Baguette Slices : Preheat your oven to 375°F (190°C). Spread the baguette slices on a baking sheet. Melt the remaining 2 tablespoons of butter and mix with 1 tablespoon of minced garlic. Brush the mixture over the baguette slices. Bake for 5–7 minutes until lightly toasted.
- Assemble the Casserole : Pour the onion and mushroom mixture into a large casserole dish. Sprinkle half of the grated Swiss cheese over the top. Arrange the toasted baguette slices in a single layer over the casserole. Sprinkle the remaining garlic over the baguette slices, followed by the rest of the Swiss cheese.
- Bake and Serve : Bake the casserole in the preheated oven for 15–20 minutes, or until the cheese is bubbly and golden. If desired, broil for an additional 1–2 minutes for extra crispiness. Remove from the oven, let cool for a few minutes, and serve warm. Enjoy this comforting and flavorful casserole as a main or side dish.
Conclusion
This French Onion Mushroom Casserole brings the savory, indulgent flavors of French onion soup to your table in a hearty baked dish. The tender onions, earthy mushrooms, and rich broth create a mouthwatering base, while the cheesy, garlicky baguette topping adds the perfect crunch. It’s the kind of recipe that feels both elegant and comforting, making it ideal for family dinners or special occasions. Serve it with a crisp green salad or a glass of wine for a restaurant-quality meal at home.
French Onion Mushroom Casserole
A comforting casserole featuring caramelized pearlonions, mushrooms, a rich broth, and toasted baguette slices layered withmelted Swiss cheese. Perfect for cozy dinners or as a show-stopping side dish.
Ingredients
- Olive oil for the pan
- 1¾ pounds pearl onions click here for how to peel pearl onions
- 8 ounces Crimini mushrooms washed, dried, and thinly sliced
- 1½ tablespoons thyme finely chopped
- 2 cups beef broth
- ½ cup dry red wine
- 5 tablespoons unsalted butter softened, divided
- 2 tablespoons all-purpose flour
- 1 approximately 2-foot skinny French baguette, thinly sliced
- 1½ tablespoons garlic minced, divided
- 1½ cups Swiss cheese grated, divided
- Sea salt and freshly ground black pepper to taste
Instructions
- Prepare the Onions and Mushrooms : Heat a drizzle of olive oil in a large skillet over medium heat. Add the pearl onions and cook for about 5–7 minutes, stirring occasionally, until they are golden and caramelized. Season with a pinch of salt and transfer to a plate. In the same skillet, add a bit more olive oil and the sliced Crimini mushrooms. Cook for 5–7 minutes, or until the mushrooms release their moisture and are browned. Add the thyme and stir for 1 minute.
- Make the Sauce : In the skillet with the mushrooms, pour in the beef broth and red wine. Bring to a simmer and let it reduce slightly for 5–6 minutes. In a small saucepan, melt 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1–2 minutes to form a roux. Slowly whisk the roux into the mushroom sauce until it thickens. Add the caramelized pearl onions back into the skillet and mix well. Season with salt and freshly ground black pepper to taste.
- Prepare the Baguette Slices : Preheat your oven to 375°F (190°C). Spread the baguette slices on a baking sheet. Melt the remaining 2 tablespoons of butter and mix with 1 tablespoon of minced garlic. Brush the mixture over the baguette slices. Bake for 5–7 minutes until lightly toasted.
- Assemble the Casserole : Pour the onion and mushroom mixture into a large casserole dish. Sprinkle half of the grated Swiss cheese over the top. Arrange the toasted baguette slices in a single layer over the casserole. Sprinkle the remaining garlic over the baguette slices, followed by the rest of the Swiss cheese.
- Bake and Serve : Bake the casserole in the preheated oven for 15–20 minutes, or until the cheese is bubbly and golden. If desired, broil for an additional 1–2 minutes for extra crispiness. Remove from the oven, let cool for a few minutes, and serve warm. Enjoy this comforting and flavorful casserole as a main or side dish.