For a slightly more sophisticated spin on mashed potatoes for our holiday menu, we reached for an unlikely candidate: celery root. A once-popular, widely available vegetable, celery root today gets little attention in American kitchens. Perhaps in part because of its intimidating appearance. When cooked and processed, however, this knobby, gnarled root could pass for a classic French potato puree. Celery root—which also goes by the name celeriac—has a delicate flavor and is far less starchy than potatoes. To balance that lightness, we paired celery root with Yukon Golds, producing a medium-bodied puree.