- 2 tbs unsalted butter
- 3 tbs corn oil
- 4 cups sliced onions
- 2 cups beef broth
- 1 tbs brown sugar
- 2 tbs apple cider vinegar
- 1 teaspoon dried thyme
- sea salt and pepper to taste
- 4 slices French bread
- 4 slices provolone or gruyere cheese
- 1 cup mozzarella cheese shredded
- Melt butter with oil in an 8 quart stock pot on medium heat. Add onions and stir occasionally until onions are deep golden brown and caramelized, about 15 minutes.
- Add salt, pepper, brown sugar, vinegar and thyme, and simmer covered for 30 minutes.
- Heat the oven broiler.
- Ladle soup into oven safe serving bowls and place one slice of bread on top of each (bread may be broken into pieces if you prefer). Layer each slice of bread with the cheese. Place bowls on cookie sheet and broil in the preheated oven until cheese bubbles and browns slightly.