Toss potatoes with butter and salt; arrange on the bottom and up the sides of a greased 13x9-in. baking dish. Bake, uncovered, at 400° for 25-30 minutes or until potatoes are almost tender. , Meanwhile, in a large skillet, cook beef over medium heat until no longer pink; drain. Sprinkle beef and corn over potatoes. Combine the soup, milk, garlic powder, pepper, onion and 1/2 cup cheese; pour over beef mixture. , Bake, uncovered, at 400° for 20 minutes or until vegetables are tender. Sprinkle with remaining cheese. Bake 2-3 minutes longer or until cheese is melted. Sprinkle with parsley if desired.