Potato Casserole

9 medium potatoes, boiled, peeled, and cooled.
Grate.
1/2 cup butter
1/3 cup chopped onion
1 can Cream of Mushroom soup
16 oz. sour cream
2 cups shredded cheddar cheese
1 tsp. salt
1/4 tsp. pepper
Mix altogether. Put in casserole dish (9X13) or 2 smaller dishes, sprayed with Pam. Bake 45 minutes at 350 degrees.