Here, horseradish gets mixed into mashed potatoes for a piquant holiday side dish.
In a large pot, bring potatoes to a boil in salted water over high, then reduce to a rapid simmer and cook until potatoes are tender when pierced with a knife, about 15 minutes. Drain and return potatoes to pot. With a potato masher, mash until potatoes are fluffy and free of large lumps. (For a smoother texture, pass potatoes through a ricer or food mill into pot.)
Meanwhile, in a small saucepan, heat cream, milk, and butter over medium-low until butter melts. Slowly pour cream mixture into potatoes, stirring until combined. Whisk in horseradish to taste and sour cream, and season with salt and pepper.
Serve this with Herb-Crusted Standing Rib Roast.