3 tablespoons butter
6 large yellow onions, peeled and sliced
8 cups beef broth
1/2 cup dry white wine
Salt, to taste
1/8 teaspoon white pepper
1 1/2 cups (6 ounces) Wisconsin Gruyere or Aged Swiss Cheese, shredded
1 sheet (1/2 package) frozen puff pastry, thawed
In a large, heavy saucepan, melt butter. Add onions, turn heat to low and sauté until onions are transparent, about 30 seconds.
Add beef broth, wine, salt and pepper. Simmer 20 minutes. Remove from heat and cool.
Before serving, preheat oven to 425°F. Ladle hot soup into 6 individual soup crocks or cups (about 1-1/2 cups in each) and top each with 1/4 cup shredded Swiss Cheese.
Cut puff pastry sheets into 6 equal squares. Place pastry square on top of bowls. Gently press pastry to the edges of the bowls to seal. Bake until pastry is golden, about 10 minutes.