Oven-Baked Onion Soup

4 tablespoons unsalted butter
6 cups yellow onions, thinly sliced
2 tablespoons all-purpose flour
6 cups beef broth
1/2 cup dry white wine
1/2 teaspoon salt
1/2 teaspoon freshly ground pepper
3 tablespoons brandy
6 slices French bread, toasted
6  slices Gruyere cheese
2 ounces Parmesan cheese, freshly grated (1/2 cup)

Melt butter in soup pot. Add onions and saute of medium heat until lightly browned.  Add flour and blend. Stir in beef broth, wine, salt and pepper. Bring to a boil. Reduce heat and simmer 10 minutes. Remove from heat and add brandy. Preheat oven to 375 degrees. Place slices of bread in the bottom of 6 individual ovenproof soup bowls. Ladle soup over bread, top with Guyere and sprinkle with Parmesan. Bake until cheese melts, about 5 minutes. Serve immediately.