1 pound ground beef
2 tablespoons finely chopped onion
2 tablespoons chili sauce
2 teaspoons Worcestershire sauce
2 teaspoons prepared mustard
4 slices process American cheese or cheddar cheese, halved diagonally
2 slices Swiss cheese, halved diagonally
4 hamburger buns, split and toasted
Lettuce leaves, sliced tomato and onion, cooked bacon strips, ketchup and mustard, optional
