Wash potatoes, removing sprouts and blemishes. Leave peels on and cut into 2-inch pieces.
Put potatoes in a large saucepan, cover with water, and bring to boil. Reduce heat and simmer until fork tender, about 30 minutes.
Drain (reserved liquid can be used in gravy, soup, bread, or rolls).
Mash with potato masher or fork. Add milk to desired consistency and salt to taste. Add margarine and stir.
To help fluff the potatoes, cover and place in saucepan over very low heat for about 5 minutes.