Patty Melts With Grilled Onions

• vidalia onions or other sweet onion
• 1 tablespoon balsamic vinegar
• cooking spray
• 1 lb extra lean ground beef
• 1/4 teaspoon salt
• 1/4 teaspoon fresh ground black pepper
• 3 tablespoons creamy mustard
• rye bread
• 1 cup shredded reduced-fat jarlsberg cheese

1. Arrange onion slices on a plate. Drizzle vinegar over onion slices. Heat a large grill pan over medium heat. Coat pan with cooking spray. Add onion to pan; cover and cook 3 minutes on each side. Remove from pan; cover and keep warm.
2. Heat pan over medium-high heat. Coat pan with cooking spray. Divide beef into 4 equal portions, shaping each into a 1/2-inch-thick patty. Sprinkle patties evenly with salt and pepper. Add patties to pan; cook 3 minutes on each side or until done.
3. Spread about 1 teaspoon mustard blend over 4 bread slices; layer each slice with 2 tablespoons cheese, 1 patty, 2 onion slices, and 2 tablespoons cheese.
4. Spread about 1 teaspoon mustard blend over remaining bread slices; place, mustard side down, on top of sandwiches.
5. Heat pan over medium heat. Coat pan with cooking spray. Add sandwiches to pan. Place a cast-iron or other heavy skillet on top of sandwiches; press gently to flatten. Cook 3 minutes on each side or until bread is toasted (leave cast-iron skillet on sandwiches while they cook).

vidalia onions, balsamic vinegar, cooking spray, extra lean ground beef, salt, fresh ground black pepper, creamy mustard, rye bread, cheese

Taken from www.food.com/recipe/patty-melts-with-grilled-onions-509228 (may not work)