French Onion Soup

This is one of my favourites: Serves 6

4 large onions, thinly sliced, I like the purple onions
4 tbsp butter
4 - 10oz cans of condensed beef broth or consomme. I prefer the consomme
1/2 cup dry sherry (optional)
2 tsps Worcestershire sauce
pepper
6 slices of french bread 1/2 inch thick, toasted
3/4 cup grated parmesan cheese
2 cups grated mozzarella cheese

In a large saucepan, cook onions in butter until tender but not brown, add consomme, sherry, worcestershire sauce and pepper and bring to a boil. Pour into 6 individual overproof bowls. Float a slice of toasted french bread in each. Sprinkle with parmesan and top with mozzarella. Place under broiler and heat until cheese bubbles. Serve with a salad and garlic bread.