1. Caramelize the Onions:

• Melt butter in a large pot over medium heat.
• Add thinly sliced onions and a pinch of salt.
• Cook slowly, stirring frequently, until onions turn deep golden brown (30–40 minutes).

2. Deglaze the Pot:

• Once onions are caramelized, deglaze the pot with a splash of wine or sherry.
• Scrape up any browned bits from the bottom for added complexity.

3. Add the Broth:

• Pour in beef stock and add thyme and bay leaves.
• Bring to a simmer, then reduce heat and let it cook gently for flavors to meld.

4. Prepare Bread and Cheese:

• Toast slices of French baguette until golden and crisp.
• Grate Gruyère or Swiss cheese for topping.

5. Assemble the Soup:

• After simmering for 30 minutes, remove herbs.
• Ladle the soup into oven-safe bowls.
• Place a slice of toasted baguette on top and generously sprinkle with grated cheese.

6. Broil to Perfection:

• Place bowls under a broiler until the cheese is bubbly and slightly browned.
• Watch carefully to prevent burning.

7. Serve Hot:

• Serve immediately, ensuring the soup is piping hot with melted and slightly golden cheese.