In large covered saucepan, cook onions in butter over low
heat (about 30 minutes), stirring occasionally. Add beef broth and 1 1/2 cups
of water and Worcestershire sauce; heat to boiling. Reduce heat, cover, and
simmer 30 minutes. Pour into individual soup bowls. Put handful of croutons in
each. Sprinkle with Parmesan cheese. Add 1 slice Mozzarella and 2 slices Swiss
cheese. Broil until golden brown. Serves 6.
