1. Caramelize the Onions

In a large pot, heat butter and olive oil over medium heat.

Add sliced onions, sugar, salt, and pepper.

Cook slowly, stirring frequently, until onions are golden brown and caramelized, about 30–35 minutes.

2. Deglaze the Pan

Add minced garlic and cook 1 minute.

Pour in white wine or sherry to deglaze, scraping up any browned bits from the bottom.

3. Add Broth and Herbs

Stir in broth, thyme, and bay leaf.

Bring to a simmer and cook for 15 minutes to let flavors meld.

Remove bay leaf before serving.

4. Prepare the Toasts

Preheat the broiler.

Place toasted bread slices on a baking sheet. Sprinkle generously with grated cheese.

Broil until cheese is bubbly and golden brown.

5. Serve