In a large mixing bowl, COMBINE ground beef, bread crumbs, salt, pepper and egg; BLEND well.
SHAPE beef mixture into patties (one per serving) about 3/4-inch thick.
COOK in skillet over medium heat, TURNING occasionally, until browned, about 10 minutes; DRAIN and discard drippings.
ADD onion, broth and mushrooms; HEAT to boiling.
REDUCE heat; COVER; let SIMMER until beef is done, about 10 minutes.
REMOVE patties from sauce; KEEP warm.
REHEAT sauce to boiling; MIX water and cornstarch; STIR into sauce.
BOIL and STIR for 1 minute; LADLE over patties.
Per Serving (excluding unknown items): 584 Calories; 32g Fat (50.2% calories from fat); 51g Protein; 21g Carbohydrate; 1g Dietary Fiber; 149mg Cholesterol; 3799mg Sodium. Exchanges: 1/2 Grain(Starch); 6 Lean Meat; 1/2 Vegetable; 4 1/2 Fat.