In a large bowl, combine the ground beef, bread crumbs, onion, egg, salt and pepper; mix well then shape into six 1/2-inch-thick oval patties. heat a large skillet over medium-high heat and place the patties in the skillet. Cook for 2 to 3 minutes per side, or until browned. In a small bowl, combine the mushroom soup, milk and mushrooms; mix well and pour over the patties. Reduce the heat to medium-low, cover and simmer for 8 to 10 minutes, or until no pink remains in the beef. Serve topped with the mushroom sauce.
GREAT GO-ALONG: While the patties are simmering, whip up some instant mashed potatoes then stir in some grated Cheddar cheese. Add a salad or steamed green veggie, and dinner's complete!