Description
This hearty Mushroom & Caramelized Onion Soup with Cheesy Toasties is a comforting and flavorful dish perfect for cozy meals. Slowly caramelized onions and sautéed cremini mushrooms create a rich base, enhanced by fresh thyme and a splash of dry white wine. Thickened with flour and simmered in beef or vegetable broth, the soup is served with crispy, cheesy baguette toasties topped with Gruyère and Parmesan cheeses, broiled to golden perfection.
Ingredients
Scale
Soup Base
- 4 tbsp unsalted butter
- 4 large yellow onions, thinly sliced
- 2 cloves garlic, finely chopped
- 2 bay leaves
- 2 sprigs fresh thyme
- 1 cup dry white wine
- ¼ cup all-purpose flour
- 8 cups beef broth (or vegetable broth)
- Salt & pepper, to taste
Mushrooms
- 1 tbsp unsalted butter
- 1 tbsp olive oil
- 1 clove garlic, finely chopped
- 24 oz cremini mushrooms, quartered
- 1 tsp fresh thyme
Cheesy Toasties
- 1 baguette, sliced
- 8 oz Gruyère cheese, grated
- ½ cup Parmesan cheese, grated
Instructions
- Caramelize Onions: Melt 4 tablespoons of unsalted butter in a large pot over medium heat. Add the thinly sliced onions, bay leaves, thyme sprigs, and a pinch of salt. Cook slowly, stirring occasionally, for 30–40 minutes until the onions turn a deep golden brown and are fully caramelized.
- Add Garlic and Deglaze: Stir in the finely chopped garlic and cook briefly until fragrant. Pour in the dry white wine to deglaze the pot, scraping up any browned bits. Allow the wine to simmer and reduce until mostly evaporated.
- Add Flour and Broth: Sprinkle the all-purpose flour over the onion mixture and cook for 2 minutes, stirring constantly. Gradually whisk in the beef or vegetable broth to avoid lumps. Bring the soup to a simmer and cook for another 20–25 minutes to let the flavors meld and the soup thicken slightly.
- Sauté Mushrooms: In a separate skillet, heat 1 tablespoon unsalted butter and 1 tablespoon olive oil over medium-high heat. Add the chopped garlic, then the quartered cremini mushrooms and fresh thyme. Sauté for 10–12 minutes until the mushrooms are nicely browned and have released their moisture.
- Prepare Cheesy Toasties: Toast the sliced baguette pieces until crisp. Top each slice with grated Gruyère and Parmesan cheeses. Place under the broiler for a few minutes until the cheese melts, bubbles, and turns golden brown.
- Serve: Ladle the hot soup into bowls and top with the mushroom mixture. Garnish each serving with a cheesy toastie, a sprinkle of fresh thyme, and some extra Parmesan cheese if desired.
Notes
- Use vegetable broth instead of beef broth to make this recipe vegetarian.
- Cooking the onions low and slow is key to developing their rich caramelized flavor.
- Broil the toasties carefully to avoid burning—watch them closely as they can brown quickly.
- Gruyère cheese adds a nutty flavor; you can substitute Swiss or mozzarella if preferred.
- Leftover soup can be refrigerated for up to 3 days; reheat gently on the stovetop.
