Peel potatoes and cook potatoes in boiling, salted water until tender. Drain water from potatoes. Mash cooked potatoes until smooth. Add remaining ingredients and beat until fluffly. Cool. Cover and place in refrigerator. May be used any time within 2 weeks. To use, place desired amount in greased casserole, dot with butter and bake in moderate oven, 350°F, until heated through, about 30 minutes. Makes 1 2 servings or 8 cups. Note: If you use the full amount, heat in a 2 quart casserole and dot with 2 T. butter.