Line a small casserole with aluminum foil, then roast several washed, unpeeled beets of uniform size, wrapped in foil, with the casserole's lid firmly on. Roast the beets slowly, at about 300°F. The length of time necessary will depend on the size of the beets, but it should take a good part of the day. The goal is to have the beets become very soft and caramelized inside. Peel them while still warm and slice about a half-inch thick. Toss in a dressing of three parts olive oil to one part balsamic vinegar. Serve on a bed of māche with the little rosettes left whole, either on individual plates or on a single platter. Drizzle any extra dressing over the greens.