Place the potatoes in a 2-quart saucepan with 1 teaspoon of the salt and cold water to cover. Bring to a boil, lower the heat and simmer, covered, until completely tender, about 30 minutes. Test the potatoes by piercing them with a paring knife -- there should be no resistance. Place in a colander and allow to drain well for several minutes. Combine the butter, heavy cream and milk in another saucepan and heat gently until the butter has melted. Keep warm. Working with the saucepan used to cook the potatoes, pass the potatoes through a food mill or a potato ricer. If you have any difficulty, add a little of the hot milk and butter to the potatoes. To serve, place the potatoes over a low fame and begin adding the warm milk mixture. Whip the potatoes with a wooden spoon or spatula while heating. When all the liquid is absorbed, season with the remaining salt and white pepper. Serve piping hot. Mashed potatoes are best served immediately, but if you are unable to do so, or need them for another recipe, keep the potatoes hot for up to 1 hour by placing them in the top of a double boiler, covered, and held over barely simmering water.