Place the potatoes into a large pot, and cover with salted water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Drain and allow to steam dry for a minute or two, and place the potatoes in a large bowl.
Bring the milk to a boil in a small saucepan over low-medium heat.
Whip the potatoes with an electric mixer until smooth; pour the boiling milk over the potatoes, and add butter, nutmeg, salt, and white pepper. Whip on Medium speed until light and fluffy.