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 it with Yukon Golds to produce a medium-bodied puree. We cooked the vegetables in a mixture of milk and half-and-half, a combination that won’t dilute or mask celery root’s flavor. A stick of butter (it is the holidays, after all) gave the puree a silky texture. We liked the flavors of thyme and garlic, but small amounts of sage, rosemary, bay and marjoram worked, too. The cooled puree can be refrigerated for two days; rewarm in a saucepan over low heat and check the seasoning before serving.