Celeriac, also called celery root, may look a bit scary, but once you slice off the gnarly skin, a versatile, semi-starchy vegetable with a mild taste of celery is revealed. Look for those that are about the size of a large grapefruit and feel heavy for their size. They lighten the texture and add another dimension to mashed potatoes.
Yield: Serves 6
4 russet (baking) potatoes, scrubbed
2 medium celeriac (celery root), peeled
¾ cup hot milk
3 tablespoons unsalted butter
Freshly ground black pepper
1. Cut the potatoes in half and the celeriac into quarters. Place in a large pot and fill with cold water so that the potatoes and celeriac are covered by a few inches. Add 1 teaspoon salt and place a smaller pot lid on the vegetables to keep them submerged. Bring to a boil. Cook until tender (vegetables should be easily pierced with a paring knife), 15 to 20 minutes. Drain and return the vegetables to the hot pot to remove excess moisture.
2. Put the potatoes and celeriac through a food mill or ricer, or mash them well using a fine potato masher. (If mashing, slide off and discard the potato skins.) Combine the vegetables with the milk and stir in the butter. Season with 1 teaspoon salt, or more to taste, and pepper. Serve immediately.
To keep potatoes piping hot for serving, place them in a metal bowl over a large saucepan or stockpot of simmering water, and cover with foil. Stir occasionally. You may need to add more milk just before serving.