Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-15 minutes or until tender. Drain., In a large bowl, mash potatoes with butter. Beat in the sour cream, cream cheese, onion powder, salt and pepper. Transfer 1-1/2 cups to a 2-cup baking dish coated with cooking spray. Bake, uncovered, at 350degrees for 30-35 minutes or until heated through., Cool remaining mashed potatoes. Freeze in 1-1/2-cup portions for up to 6 months., To use frozen potatoes: Thaw in the refrigerator. Bake as directed.