Deluxe Mashed Potatoes

5 pounds potatoes
8 oz. cream cheese
8 oz. sour cream
1 ts. salt
1 ts. onion salt
3/4 ts. pepper
3 Tbs. butter

Peel and cube the potatoes; place in pan and cover with water. Cook over medium heat until very tender. Mash until smooth (do not add milk or butter). Stir in cream cheese, sour cream, onion salt, salt, and pepper. Place in 1 quart baking dish. Dot with butter. Cover and bake at 350 degrees for 35-40 minutes or until heated through.