Cheesy Potato Beef Bake

1 pound ground beef
2 cans (4 ounces each) mushroom stems and pieces, drained, optional
2 packages (5-1/4 ounces each) au gratin potatoes
4 cups boiling water
1-1/3 cups milk
2 teaspoons butter or margarine
1 teaspoon salt
1/2 teaspoon seasoned salt
1/2 teaspoon pepper
1 cup (4 ounces) shredded cheddar cheese

In a skillet over medium heat, cook beef until no longer pink; drain. Place in a greased 13-in. x 9-in. x 2-in. baking pan. Top with mushrooms. Combine potatoes and contents of sauce mix packets, water, milk, butter, salt, seasoned salt and pepper.

Pour over beef and mushrooms. Cover and bake at 400° for 30 minutes or until heated through. Sprinkle with cheese. Bake, uncovered, for 5 minutes or until cheese is melted. Let stand 10 minutes before serving. Makes 8 servings.