2 Tablespoons finely chopped onion
2 Tablespoons ketchup
2 teaspoons prepared mustard
1/2 teaspoon salt
1/4 teaspoon pepper
1 pound lean ground beef
1/2 cup cheddar cheese, finely shredded
4 hamburger buns
1. In a small bowl, combine the first five ingredients. Crumble beef over mixture and mix well. Shape into four thin patties. Sprinkle cheese over two patties; top with remaining patties and press edges firmly to seal.
2. Grill, covered, over medium heat for 6 minutes on each side or until a meat thermometer reads 160° and juices run clear. Serve on buns with lettuce and tomato if desired.