1 medium onion, thinly sliced
1 teaspoon balsamic vinegar
1/2 lb. lean ground beef
1/8 teaspoon salt
dash pepper
2 tablespoons Dijon mustard
4 slices rye bread
1/2 cup shredded Jarlsberg or other Swiss cheese
Preheat electric grill or pannini pan. Sprinkle onion with balsamic vinegar. Spray pan with nonstick cooking spray and add onion. Cook about 3 minutes; remove and keep warm. Divide beef into two patties and sprinkle with salt and pepper. Add patties to pan; cook about 4 minutes or until done. Spread 1 teaspoon mustard over 2 bread slices; layer each slice with 2 tablespoons cheese, 1 patty, half of the onion, and 2 more tablespoons cheese. Spread about 1 teaspoon mustard on remaining bread slices; place, mustard side down, on top of sandwiches. Wipe pan, if necessary. Add sandwiches, and cook about 3 minutes or until bread is lightly browned and crusty. Makes 2.
