How to Make It
In a large pot, cover potatoes by at least 1 inch with cold salted water. Bring to a boil, uncovered, over high heat. Cook over medium-high heat until very tender when pierced with a knife, about 25 minutes. In a small pan over medium-low heat, warm half-and-half, butter and horseradish, stirring occasionally, until butter melts and bubbles begin to form around edge of pan.
Drain potatoes, return to pot and mash well. Pour in horseradish mixture and stir well. Season with salt and pepper and serve.