Potato Sausage Casserole

1 lb. bulk sausage
1/2 cup chopped onion
3 cups sliced potatoes
1 can cream of mushroom soup
3/4 cup milk
1/2 tsp. salt
1/2 tsp. pepper
1 cup grated cheese

Boil potatoes in their jackets, cool and slice (this can be done ahead). Meanwhile brown sausage and onion in skillet. Mix together milk, soup, salt and pepper. In a 2 quart casserole sprayed with non-stick cooking spray, layer half the potatoes, half the soup mixture and half the sausage. Repeat, ending with sausage. Top with grated cheese and bake at 350ºF for 45 minutes or until cheese is melted and casserole is hot through.