Smashed Potatoes and Celery Root with Horseradish and Parmesan

Celery root teams up with potato and spicy horseradish for a satisfying smash. Popular in Europe and less used in the U.S., celery root, also known as celeriac, is the dark horse of tubers. Don’t let it’s gnarly, bulbous exterior put you off. Once you peel away the skin a milky white interior is revealed, fragrant with celery. Its smooth and mellow flavor adds a delightful dimension to mashed potatoes, gratins, soups and stews.

Smashed Potatoes with Celery Root and Horseradish and Parmesan

Nutrient-rich potato skins fleck this side dish, adding flavor and texture. Peel the potatoes if you prefer a smoother texture.  Serves 6-8.

1 1/2 pounds yukon gold potatoes, cut into 1-inch pieces
1 1/2 pounds celery root, peeled, cut into 1-inch pieces
Bouquet garni: 1 bay leaf and 3 thyme sprigs, tied in cheese cloth with kitchen string
Salt
1/4 cup unsalted butter, cut into pieces
3/4 cup sour cream or creme fraiche
3 tablespoons finely grated fresh horseradish, divided
3 tablespoons finely grated Parmigiano-Reggiano cheese, divided
1 teaspoon black pepper

Combine potatoes and celery root in large pot. Cover with cold water. Add bouquet garni and 1 teaspoon salt. Bring to a boil, then reduce heat to a simmer. Cook, partially covered until potatoes and celery root are very tender, about 20 minutes. Drain thoroughly. Transfer to a large bowl. Add butter and smash with a potato masher. Stir in sour cream, 2 tablespoons horseradish, 1 tablespoon cheese and black pepper. Add more salt to taste. Transfer potatoes to a buttered casserole or baking dish. (Potatoes may be prepared up to one day in advance to this point. Let cool completely, then cover with plastic wrap and refrigerate.)

Preheat oven to 350 F. (180 C.) Mix 1 tablespoon horseradish with 2 tablespoons cheese in a small bowl. Sprinkle over top of potatoes. Bake in oven until top is tinged golden brown and potatoes are heated through, about 25 minutes. Serve immediately.