4 lb large yellow-fleshed potatoes such as Yukon Gold, peeled and quartered
1 3/4 C. half-and-half
3/4 stick (6 tablespoons) unsalted butter, cut into tablespoon pieces
1 1/2 t. salt
1/2 t. black pepper
1/4 C. drained Kelchner’s horse-radish
Special equipment: a potato ricer or a food mill fitted with medium disk
Cover potatoes with salted cold water by 2 inches in a 5-quart heavy pot, then simmer, uncovered, until very tender, about 25 minutes.
While potatoes are simmering, bring half-and-half, butter, salt, and pepper just to a simmer, stirring until butter is melted. Keep hot, covered.
Drain potatoes in a colander, then immediately force through ricer into a large bowl. Stir in hot milk mixture, then horseradish.
If you don't have a ricer or food mill, you can use a handheld masher, but the consistency of the potatoes won't be as smooth.
Mashed potatoes can be made 1 day ahead and chilled, covered. Bring to room temperature, then reheat in a microwave or double boiler, stirring occasionally.