This classic soup is made with caramelized onions, beef broth, and Gruyère cheese. The smoky flavor from the Dutch oven will add a depth of flavor to this soup.
For a richer flavor, use homemade beef broth instead of store-bought.
If you don't have dry sherry, you can substitute it with white wine.
You can also add other vegetables to this soup, such as carrots or celery.
Serve the soup with a side salad or crusty bread.