Buttermilk Mashed Potatoes with Horseradish Recipe

Scrub the potatoes and leave them wet. Prick each potato once with a fork and wrap it in a sheet of microwave-safe paper towel, tucking in the ends. Arrange the potatoes in the microwave, end to end and 1 inch apart with the tucked-in ends down, microwave them at high power (100%) for 8 to 10 minutes, or until they yield to gentle pressure, and let them stand, wrapped, for 5 minutes.
In a 1-quart microwave-safe bowl combine 2/3 cup of the buttermilk, the butter, the horseradish, and salt and pepper to taste and microwave the mixture, covered, at high power for 2 minutes. Peel the potatoes, while they are still hot force them through a ricer or the medium disk of a food mill into the buttermilk mixture, and combine the mixture well, adding some of the remaining buttermilk if necessary to reach the desired consistency.