Mix ground chuck, bread crumbs, salt, pepper and egg; shape into 3 large patties, about 1/2-inch thick.
Cook patties in large skillet over medium heat, turning occasionally, until browned, about 10 minutes; drain. Add broth, onion, and mushrooms. Heat to boiling; reduce heat. Cover and simmer until patties are done, about 15 minutes.
Remove patties; keep warm. Heat onion mixture to boiling. Mix water and cornstarch; stir into onion mixture. Boil and stir 1 minute. Pour over patties.