We like this one:
FRENCH ONION SOUP
1/4 cup (1/2 stick) butter
6 onions (about 3 pounds), sliced
6 garlic cloves, sliced
1/2 cup dry white wine
3 cups canned low-salt chicken broth
3 cups canned beef broth
1 teaspoon Dijon mustard
4 sourdough bread slices, toasted
1 cup grated Swiss cheese
1/2 cup grated Parmesan
Melt butter in heavy large saucepan over medium heat. Add onions and garlic and sauté until very tender and brown, about 45 minutes. Add wine and simmer until reduced to glaze, about 3 minutes. Stir in chicken broth, beef broth and mustard. Simmer 20 minutes. Season to taste with salt and pepper. (Can be prepared 1 day ahead. Refrigerate. Return soup to simmer before continuing.)
Preheat broiler. Ladle soup into broilerproof bowls. Top each with slice of toast and grated cheeses. Broil until cheeses melt and bubble.
Serves 4.