Place the potatoes in a medium stockpot and add enough water to cover by 2 inches. Place over high heat and bring to a boil. Reduce to a simmer and cook until tender when pierced with the tip of a knife, 15 to 20 minutes.
In a small saucepan, combine milk and butter. Place over medium heat until milk is warm and butter is melted.
Drain cooked potatoes well, and return to stockpot. Add milk mixture and, using a potato masher, mash to desired consistency. Alternatively, pass potatoes through the medium die of a ricer into a medium bowl, add milk mixture and stir to combine. Season with salt and pepper.