In a large kettle cover 1 1/2 pounds turnips and 1 pound potatoes, all peeled, with cold water, bring the water to a boil over moderate heat, and simmer the vegetables, covered, for 30 minutes. Add 1 1/2 pound carrots and 1 tablespoon salt and simmer the vegetables, covered, for 40 minutes, or until they are tender. Drain the vegetables and in the kettle steam them, covered, shaking the pan until they are dry. Puree the vegetables through a food mill into a bowl and beat in 3/4 stick (6 tablespoons) butter, softened, 1/4 cup firmly packed light brown sugar, and freshly grated nutmeg, salt, and white pepper to taste. Transfer the puree to a heated serving dish.
Comment: I don't following the cooking times. I cook all the vegetables together for about 45 minutes. I mash the mixture with a potato masher and leave it rather chunky.