Combine the turnips, milk, thyme and garlic in a medium saucepan. Set over medium heat and partially cover the pan. Bring to a gentle simmer and cook for 20 to 30 minutes, until the turnips are tender-the tip of a paring knife should go through without resistance.
Drain the turnips, reserving the cooking liquid, and transfer to a food processor (discard the time sprigs). Add about 1 cup of the reserved cooking liquid and the butter, season with plenty of salt and pepper and puree until smooth. Add more of the liquid, if necessary. Serve hot.
Recipe courtesy of Tyler Florence for Food Network Magazine