Celeriac & Parsnip Mash

Place celeriac and parsnips in a large saucepan; cover with lightly salted water. Place potato in a medium saucepan; cover with lightly salted water. Bring both saucepans to a boil over medium-high heat. Reduce heat to low, cover, and simmer gently until the vegetables are very tender when pierced with a fork, about 20 minutes for the potato and 30 to 40 minutes for the celeriac and parsnips.

When the potato is tender, drain and transfer to a large bowl. Mash with a potato masher. Cover and keep warm. When the celeriac and parsnips are tender, drain and transfer to a food processor; process until smooth, stopping once or twice to scrape down the sides. Add the puree to the potato.

Meanwhile, combine broth and oil in a saucepan (or measuring cup) and heat on the stovetop (or in the microwave) until steaming. Stir into the puree, along with 2 tablespoons chives, yogurt, mustard, salt and pepper. Stir in Parmesan. Garnish with the remaining 1 tablespoon chives. Serve hot.