Simple Salisbury Steak

1 can cream of mushroom soup, divided
1 lb. ground beef
1/3 cup dry bread crumbs
1 egg, beaten
1/4 cup finely chopped onion
1 1/2 cups sliced mushrooms
1. In bowl, mix thoroughly 1/4 cup of the soup, beef, bread crumbs, egg and onion. Shape firmly into 6 patties.
2. In skillet over medium-high heat, cook patties, a few at a time, until browned on both sides. Spoon off fat.
3. Stir in remaining soup and mushrooms; return patties to skillet. Reduce heat to low. Cover; simmer 20 min. or until done, turning patties occasionally.