T.G.I. Friday's French Onion Soup

2 Tablespoons butter or margarine
4 cups sliced onion
3 cups beef broth
1−1/2 cups water
1 Tablespoon cooking sherry
1 Tablespoon Worcestershire sauce
1/4 teaspoon black pepper
1 dash dried thyme
1 cup soft croutons
1/2 cup shredded mozzarella cheese

Melt butter in saucepan over low heat.
Add onions and cook 20 minutes, stirring occasionally.
Add beef broth, water, sherry, Worcestershire sauce, pepper, and thyme to pot.
Increase heat and bring to boil, then reduce heat.
Cover and simmer for 5 minutes.
Divide into bowls.
Top with croutons, then mozzarella.
Broil until cheese melts and begins to brown.