Beefy Potato Casserole

1 (22 ounce) package frozen mashed potatoes
2 tbsp butter
1 tsp salt, divided
1 pound lean ground beef
1 small onion, chopped
1/2 tsp seasoned pepper
2 cups (8 ounces) shredded Cheddar cheese, divided
1 (11 ounce) can whole kernel corn, drained
1 (10 3/4 ounce) can cream of mushroom soup, undiluted
1/2 cup milk

Prepare mashed potatoes according to package directions. Stir in butter and 1/2 tsp salt; set aside.

Cook ground beef, onion, and seasoned pepper in a large skillet over medium high heat, stirring until beef crumbles and is no longer pink; drain and return to skillet. Add 1 cup cheese, corn, soup, milk, and remaining 1/2 salt, stirring well.

Pour beef mixture into a lightly greased 13 X 9 inch baking dish. Spread mashed potatoes evenly over beef mixture.

Bake, covered, at 350 for 20 minutes; sprinkle with remaining 1 cup cheese and bake 10 more minutes.