Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and simmer for 10-15 minutes or until tender. Drain. , Mash potatoes with 3 tablespoons of butter. Stir in the cream cheese, sour cream, onion salt, garlic powder and pepper until smooth., Spoon into a greased 13-in. x 9-in. baking dish. Melt remaining butter; drizzle over the top. Cover and freeze for up to 1 month. Or bake, uncovered, at 350° for 30-35 minutes or until heated through. , To use frozen potatoes: Thaw in the refrigerator. Bake as directed.