Ingredients

• 2 tablespoons (1/4 stick) butter
• 2 pounds onions, thinly sliced
• 3 14 1/2-ounce cans beef broth
• 1/2 cup dry red wine
• 1 1/3 cups seasoned croutons
• 4 thin slices Swiss cheese
• 4 tablespoons grated Parmesan cheese

Instructions

1. Melt butter in heavy large pot over medium-high heat. Add onions; cook until deep brown, stirring frequently, about 25 minutes. Add broth and wine; boil until soup is slightly reduced and flavors blend, about 10 minutes. Season with salt and pepper.
2. Meanwhile, preheat oven to 500°F. Put 4 deep ovenproof bowls on baking sheet. Put 1/3 cup croutons in each bowl.
3. Ladle soup over croutons. Top with cheeses. Bake soup until heated through and cheeses melt, about 8 minutes.