Place the butter in a large stock and set on low heat until the butter melts. Add the bay leaf and the onions. Cook over low heat until the onions become translucent. Add the pepper and the onion. Mix until well combined.
 
Pour the beef broth and water over the onions. Continue cooking over low heat for 45 to 60 minutes. You want the broth to be thick enough that it looks like soup without over reducing the soup.
 
Place the slices of bread on a baking sheet. Set in the oven with the oven turned to the broiler setting. Once the top of the soup turns light brown, flip the bread over and cook until golden brown on the other side. Remove from the oven.
 
Transfer the soup mixture into six ovenproof crocks or bowls. Top each bowl with a piece of the bread and a slice of the cheese. Arrange each bowl on a baking sheet. Slide the sheet back under the broiler until the cheese melts. 
If you want more of a rich cheese flavor, consider adding a small amount of Parmesan cheese to the top of each soup dish before broiling.