Although it means more ingredients, I like to use equal parts of chicken and beef stock. Personally I am also a sherry fan, and I like my soup onions to be Spanish. I also like to broil the soup until the cheese caramelizes. They crocks are a pain to clean after... Having a very high onion to broth ratio is key. Don't think "Wow that's way to many onions" Cook and cook and cook them down to that deep amber color. Also don't cut them thin. You can easily reduce a large onion to the size of a golf ball, so size accordingly.