French Onion Soup

2 Tbsp butter
2 cups onion, chopped
4 cups beef broth
2 Tbsp wine vinegar, optional
1 tsp Worcestershire sauce
pepper, to taste
2/4 cup mozzarella cheese
4 slices French bread

Saute onions in butter for 8-10 minutes. Add broth, vinegar, Worcestershire sauce and pepper. Simmer for 10 minutes. Place soup in 4 ovenproof bowls. Add a slice of toasted French bread to each. Then top with cheese. Broil in oven until cheese is bubbly and beginning to brown.

Variation: Instead of putting soup in ovenproof bowls, just heat it on the stove and put into individual serving bowls. Place toasted bread slices on a baking sheet and top with cheese. Broil in the oven. Then place the bread into the soup bowls.

Serve with a green salad for a complete meal.