- 2 1/2 lb yellow-fleshed potatoes such as Yukon Gold
- 3 lb turnips or rutabagas, peeled and cut into 2-inch pieces
- 6 tablespoons unsalted butter, softened
- 2 tablespoons horseradish cream or drained bottled horseradish, or to taste
- 2 to 4 teaspoons sugar
- 1/2 cup chopped fresh flat-leaf parsley
- Cover potatoes with salted cold water by 2 inches in a large pot and simmer, uncovered, until very tender, 20 to 30 minutes (depending on size of potatoes). Drain potatoes in a colander and, when just cool enough to handle, peel. Transfer potatoes to a bowl.
- While potatoes are cooking, cover turnips with salted cold water by 2 inches in a large pot and simmer, uncovered, until very tender, 10 to 20 minutes (depending on freshness of turnips).
- Drain turnips in colander and immediately add to warm potatoes, then mash with butter and horseradish. Season with sugar (to taste), salt, and pepper and stir in parsley.