Servings: 6

6 large yellow onions, cut in large dice 6 large yellow onions, cut in large dice
1/4 cup unsalted butter ¼ cup unsalted butter
salt and pepper to taste salt and pepper to taste
1 bay leaf 1 bay leaf
1 tsp balsamic vinegar 1 tsp balsamic vinegar
1 tsp vanilla extract 1 tsp vanilla extract
4 cups high-quality beef broth 4 cups high-quality beef broth
4 cups high-quality chicken broth 4 cups high-quality chicken broth
shredded cheese shredded cheese

For the onions: subheading: 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: subheading: 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.