Mashed Potato Mountain

Boil 2 lbs. potatoes (peeled and quartered) with 1 whole head of garlic cloves (peeled only) in lightly salted water for about 25 minutes (or until potatoes are fork-tender). Drain and mash. Using hand beaters, whip in 2 T. of margarine, 1/3 cup sour cream, 1/3 cup buttermilk and 2 Tbs. prepared horseradish, adding salt and pepper to taste.