Turnip Mashed Potatoes

Slice potatoes 1/4 inch thick, leaving skin on. Keep sliced potatoes in a bowl of cold water until ready to cook to prevent browning. Peel turnips and cut into 1/4 inch slices. Boil potatoes in salted water for about five minutes before adding turnips. Cook turnips and potatoes in boiling water for 15 minutes or until fork-tender. Drain. Whip unpeeled cooked potatoes with electric mixer; mix until moderately smooth. Don't over beat them; a few lumps are nice. Heat cream over low flame until warm. Add hot cream, sour cream and salt and pepper to taste. Whip until mixed. Adjust thickness by adding more cream, if desired. Top serving with a generous amount of butter pats and a sprig of thyme.