Bring a large pot of water to a boil. Add the potatoes and salt, to taste. Boil until fork tender. Drain well in a colander.

Return the pot to the stove and add the milk and butter and warm over medium-low heat. While the butter and milk are warming, rice the potatoes into the milk mixture. When all potatoes are riced, add the sour cream and season to taste with salt and pepper. Stir with a wooden spoon and serve immediately.