Vegetarian French Onion Soup

Instructions

1. Caramelize the onions
   In a large, heavy-bottomed pot, heat butter and olive oil over medium heat. Add sliced onions, salt, and sugar. Cook for 45-50 minutes, stirring occasionally, until onions are deeply caramelized to a rich golden-brown color. Be patient as this slow process develops the soup's deep flavor.
2. Create the soup base
   Sprinkle flour over caramelized onions and cook for 2-3 minutes, stirring constantly. Gradually add vegetable broth while stirring to prevent lumps. Add white wine, bay leaves, and thyme sprigs. Bring to a simmer.
3. Simmer and season
   Reduce heat to low, cover partially, and simmer for 30 minutes to allow flavors to meld. Remove bay leaves and thyme sprigs. Stir in balsamic vinegar and soy sauce for depth of flavor. Taste and adjust seasoning if needed.
4. Prepare the bread topping
   While soup simmers, preheat your oven's broiler. Place baguette slices on a baking sheet and toast until lightly golden on both sides, about 2-3 minutes per side.
5. Assemble and broil
   Ladle soup into oven-safe bowls placed on a baking sheet. Float 1-2 toasted baguette slices on top of each bowl of soup. Generously sprinkle with grated Gruyère cheese, ensuring the bread is completely covered and some cheese falls into the soup.
6. Finish under the broiler
   Place the baking sheet with soup bowls under the broiler for 3-5 minutes, until cheese is melted, bubbly, and lightly browned. Watch carefully to prevent burning. Remove from broiler and let cool slightly before serving.