1. Drain the yogurt to 1½ cups. Cut off all but 1 inch of the beet stalks and leave the roots intact. Rinse the beets well but do not peel. Cook the beets in boiling salted water until tender, 25 to 35 minutes. Drain, slip off the skins under cold running water, and cut away the root ends and stalks. Coarsely grate the beets, using the shredding disk of a food processor or the large holes of a hand grater.