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 sour cream, cream cheese, onion powder, salt and pepper. Transfer to a greased 13x9-in. baking dish. Bake, uncovered, at 350° until heated through, 30-35 minutes. Or, transfer 1-1/2 cup portions to greased 2-cup baking dishes. Cover and freeze up to 6 months. , To use frozen potatoes: Thaw in the refrigerator overnight. Bake at 350° until heated through, 30-35 minutes.