Place 8 medium-size potatoes (about 4 pounds) peeled, rinsed and quartered with 8 medium sized turnips (about 2 pounds) peeled and cut into eighths in a large saucepan and cover with about 2 inches of lightly salted cold water    Bring to a boil, then cover and boil slowly over medium-high heat for about 25 minutes, or until very tender when pierced with a fork    Drain well and mash with a potato masher or beat with an electric mixer    Beat in 1/4 lb butter softened, 1/4 cup half-and -half milk or light cream, 1/2 tsp salt, 1/2 tsp ground white pepper    Set aside-uncovered-until close to serving time    Then rewarm over very low heat, beating constantly.    Turn into a serving bowl and sprinkle lightly with chopped fresh parsley or paprika for garnish