- 6 large yellow onions, cut in large dice
- 1/4 cup unsalted butter
- salt and pepper to taste
- 1 bay leaf
- 1 tsp balsamic vinegar
- 1 tsp vanilla extract
- 4 cups high-quality beef broth
- 4 cups high-quality chicken broth
- shredded cheese
- For the onions:
- Preheat oven to 425F.
- Melt the butter in a large pyrex in the oven. Stir in onions and season with salt and pepper, mixing until onions are coated in butter. Cook in oven until tender and well browned - about one hour - stirring every 15 minutes.
- Transfer onions to a skillet and cook over medium heat, stirring constantly, until the bottom of the pan starts to brown - about 5 minutes. Add vinegar and vanilla into the pan, bringing to a boil while scraping browned bits of onion off the bottom of the pan with a wooden spoon.
- For the soup:
- Place caramelized onions in a large soup pot. Pour in chicken broth, beef broth, and bay leaf. Bring to a boil, skimming off any foam and fat that appear on top. Reduce heat to low and simmer for about an hour. Season with salt and pepper to taste.