Prepare dry-French bread slices - one per bowl.
Heat two tablespoons butter or margarine in a fry pan over medium heat.
Add six large yellow onions, thinly sliced and cook, stirring occasionally until soft and caramel-coloured but not browned (about 30 - 40 minutes)
Pour about on cup of broth (using three 14½ oz cans)of regular-strength beef broth soup over onions.
Stir to blend in one tablespoon flour. Add remaining beef broth and one cup water and one third cup of dry red or white wine.
Salt and pepper to taste. Bring above to boil.
Cover with lid reduce heat. Simmer for 30 minutes.
Ladle hot soup into six over proof soup bowls. Place slice of dry French bread on top of each. Add a slice of Swiss or Mozzarella cheese and sprinkle top with parmesan cheese. Place bowls in over for ten minutes at 425 degrees or in microwave. Turn oven up to broil, and broil for about four minutes until cheese is lightly browned.