Vegetarian Mushroom Soupe à l'oignon

Caramelizing Onions

1. 1Melt butter in a large heavy-bottomed pot or Dutch oven over medium-low heat. Add the sliced onions and a pinch of salt.
2. 2Cook, stirring occasionally, for 40-50 minutes, or until the onions are deeply caramelized and a rich golden brown. Be patient, as this step is crucial for flavor.

Building the Soup

1. 1Add sliced cremini mushrooms to the caramelized onions and cook for an additional 5-7 minutes, until softened and browned.
2. 2Pour in the dry white wine, scraping any browned bits from the bottom of the pot with a wooden spoon. Let it simmer until almost completely reduced, about 3-5 minutes.
3. 3Stir in the vegetable broth, thyme sprigs, and bay leaf. Bring the soup to a gentle simmer, then reduce heat to low, cover, and cook for at least 20 minutes to allow the flavors to meld.
4. 4Remove the thyme sprigs and bay leaf. Season with salt and black pepper to taste.

Serving

1. 1Preheat your oven's broiler. Arrange baguette slices on a baking sheet and toast lightly until golden brown.
2. 2Ladle the hot soup into oven-safe bowls. Float a toasted baguette slice (or two) on top of each bowl.
3. 3Generously sprinkle shredded Gruyère cheese over the baguette and soup.
4. 4Place the bowls under the broiler for 2-4 minutes, or until the cheese is melted, bubbly, and golden brown. Watch carefully to prevent burning.
5. 5Serve immediately and enjoy the rich, savory flavors.