4 large onions, thinly sliced
2 tablespoons butter
1 tablespoon olive oil
1 teaspoon salt
1 teaspoon sugar
2 cloves garlic, minced
1 tablespoon all-purpose flour
6 cups beef broth
1/2 cup dry white wine
1 bay leaf
1/2 teaspoon black pepper
1 teaspoon thyme
Baguette slices
1 1/2 cups grated Gruyère cheese
Melt butter and olive oil in a large pot over medium heat
Add onions and salt
Cook onions slowly until soft and caramelized
Add sugar and garlic
Stir in flour and cook for 1 minute
Add wine and scrape the bottom of the pot
Add beef broth, bay leaf, pepper, and thyme
Simmer for 20 to 30 minutes
Remove bay leaf
Ladle soup into oven-safe bowls
Top with baguette slices
Add grated cheese on top
Broil until cheese is melted and golden
Serve hot