(From "More Vegetables, Please" by Janet Fletcher. Harlow and Ratner, Emeryville, California; $16.95, 1992) Peel the rutabagas, removing all traces of the thick skin. Cut them into 1 cm cubes. Peel the carrots and slice them about 1 cm thick. Scrub the potatoes well but do not peel them; cut them into pieces about the same size as the rutabagas. Bring a large pot of salted water to a boil over high heat. Add the rutabagas and cook 5 minutes, then add the remaining vegetables and cook until they are soft enough to mash but not mushy, about 15 more minutes. Drain thoroughly in a colander. Put the hot vegetables in a clean pot and shake the pot over moderate heat until the vegetables are completely dry. Remove the pot from the heat, add the butter in small pieces, and mash the vegetables gently with a potato masher; they should be mashed, not pureed. Season to taste with salt and pepper. Transfer to a warm serving bowl. Garnish with parsley if desired.