French bread, cut into thick slices Parmesan cheese, grated In a heavy saucepan, melt the butter/margarine. Add onions and cook until they are golden, do not brown. Add the undiluted beef broth, 1 soup can of water, Coca-Cola, salt, vinegar, and pepper. Cover and simmer 20 to 25 minutes. . In a broiler, toast one side of the French bread slices. Turn and generously sprinkle with the Parmesan cheese. Toast until browned. Into deep bowls, ladle the soup and top with the toast, cheese-sided up. Makes 4 servings or about 6 cups.