# Components:
→ Vegetables
01 - 3 large yellow onions, thinly sliced
02 - 10 oz cremini or button mushrooms, sliced
03 - 2 cloves garlic, minced
04 - 1 stalk celery, finely chopped
→ Dairy
05 - 2 tbsp unsalted butter
06 - 1/2 cup heavy cream
→ Liquids
07 - 4 cups vegetable broth
08 - 1/4 cup dry white wine (optional)
→ Seasonings
09 - 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
10 - 1 bay leaf
11 - Salt and freshly ground black pepper, to taste
→ Garnish (optional)
12 - 4 slices baguette, toasted
13 - 2 oz Gruyère or Swiss cheese, grated
14 - Fresh parsley, chopped
# Directions:
01 - In a large heavy-bottomed pot, melt unsalted butter over medium-low heat. Add sliced onions and a pinch of salt. Cook, stirring frequently, until the onions are deeply caramelized and golden brown, approximately 25 to 30 minutes.
02 - Add minced garlic and finely chopped celery to the pot; sauté for 2 minutes until fragrant.
03 - Stir in sliced mushrooms and cook until softened and lightly browned, about 8 minutes.
04 - Pour in dry white wine if using, deglazing the pot and scraping up any browned bits. Allow the wine to reduce by half, about 2 minutes.
05 - Add vegetable broth, thyme leaves, and bay leaf. Bring to a gentle simmer and cook uncovered for 10 minutes to blend flavors.
06 - Remove the bay leaf. Lower the heat and stir in heavy cream. Simmer for 2 to 3 minutes, taking care not to boil. Taste and adjust seasoning with salt and black pepper.
07 - For a traditional gratinée finish, ladle soup into oven-safe bowls, top each with a toasted baguette slice, sprinkle with grated Gruyère, and broil until cheese is bubbly and golden.
08 - Garnish the soup with chopped fresh parsley before serving.
