Yield: Serves 4
- 1/4 cup (1/2 stick) butter
- 6 onions (about 3 pounds), sliced
- 6 garlic cloves, sliced
- 1/4 cup apple cider vinegar
- 3 cups canned low-salt chicken broth
- 3 cups canned beef broth
- 1 teaspoon Dijon mustard
- 4 sourdough bread slices, toasted
- 2 cup grated Gruyere (Emmentalier is also nice)
Melt butter in heavy large saucepan over low to medium-low heat. Add onions and garlic and sauté until very tender and brown, about 1-1 1/2 hours. Add vinegar 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 your broiler. Place the toast on cookie sheet and liberally top with cheese. Broil until the cheese has melted and browned to your liking.
Ladle the soup in a bowl and serve hot with the toast on the side.