Prep 10 mins
Cook 50 mins
- 3 tablespoons butter
- 4 onions, sliced thinly
- 2 tablespoons sugar
- 2 (14 1/2 ounce) cans beef broth
- 1 tablespoon balsamic vinegar or 1 tablespoon red wine vinegar
- salt and pepper
- 4 slices toasted French bread
- 1 cup grated swiss cheese
- In large soup pot over medium heat, melt the butter.
- Add the onions, cover and slowly cook until soft and translucent, stirring occasionally, about 15 minutes.
- Add sugar and continue to cook until caramelized and rich brown in color, about 10 more minutes.
- Add broth, vinegar, and salt and pepper to taste.
- Simmer, covered for 20 minutes.
- Heat broiler.
- Ladle soup into 4 oven proof bowls.
- Top each with a piece of toasted bread and 1/4 of the cheese.
- Broil until cheese is melted and golden.
- Be careful removing bowls from boiler.