30 minutes active; 4 hours inactive to prepare, Serves 8
4 pounds yellow onions, peeled and chopped
10 cups beef broth
1 baguette, sliced diagonally and toasted
1 bay leaf
1 1/2 cups Gruyere or Swiss cheese, grated or sliced
1/2 cup (1 stick) unsalted butter, melted
1/4 cup all-purpose flour
2 tablespoons extra-virgin olive oil
2 tablespoons balsamic vinegar
1 tablespoon Worcestershire sauce
kosher salt and freshly ground pepper, to taste
Minced chives, for garnish
Step 1: Place chopped onions, butter, and olive oil in a large skillet or pot, and cook over medium heat for 10-15 minutes, or until onions start to caramelize.
Step 2: In a small bowl, whisk flour into balsamic vinegar and Worcestershire sauce and mix until smooth.
Step 3: Transfer onions to slow cooker. Pour in beef broth, bay leaf, salt, pepper, and flour mixture, and stir well to combine.
Step 4: Cover and cook on low for 6-8 hours, or on high for 3-4 hours.
Step 5: Ladle soup into oven proof bowls, top each with 1 slice of bread and cheese, and broil, about 5 minutes or until cheese is melted and bubbly.
Step 6: Garnish with chives, serve hot and enjoy!