1. Caramelize the onions:
In a large pot, heat the butter and olive oil over medium heat.Add the onions and sugar. Cook, stirring frequently, for 30–40minutes, until the onions become soft, golden, and caramelized. If the onionsstart to brown too quickly, lower the heat.

2. Add garlic and herbs:
Once the onions are caramelized, add the garlic, thyme, and bayleaf. Cook for another 1–2 minutes until the garlic is fragrant.

3. Deglaze and simmer:
Pour in the white wine (if using) and cook for 2–3 minutes to deglaze the pot, scraping up any browned bits. Add the beef broth and Worcestershire sauce (if using). Bring the soup to a simmer, then reduce the heat and cook for 15–20 minutes to allow the flavors to blend. Season with salt and pepper to taste.

4. Prepare the bread:
While the soup is simmering, preheat your oven to 180°C (350°F). Place the baguette slices on a baking sheet and toast them in the oven for about 10 minutes, or until golden brown and crispy.

5. Assemble the soup:
Ladle the hot soup into oven-safe bowls. Place a slice of toasted bread on top of each bowl, and generously sprinkle with Gruyère cheese.

6. Melt the cheese:
Place the bowls under the broiler for 3–5 minutes, or until the cheese is bubbly and golden brown. Keep an eye on them to avoid burning.

7. Serve:
Carefully remove the bowls from the oven, and let them cool slightly before serving. Garnish with additional thyme if desired.

‍