- 1/2 cup unsalted butter
- 2 tablespoons olive oil
- 4 cups sliced onions
- 4 (10.5 oz) cans beef broth
- 2 tablespoons dry sherry
- 1 teaspoon dried thyme
- 4 slices French bread
- 4 slices provolone cheese
- 2 slices Swiss cheese, diced
- Melt butter with olive oil in pot over medium heat. Add onions and continually stir until tender and translucent.
- Add beef broth, sherry, and thyme. Simmer 30 minutes.
- Ladle soup into oven safe bowls and place one slice of bread on top of each. Layer bread with slices of provolone and a 1/2 slice Swiss.
- Broil in the preheated oven until cheese browns slightly.
