Place 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.

Mash potatoes in a large bowl with milk and butter. Season with salt and pepper.

Whip potatoes using an electric mixer set on medium until smooth, 3 to 4 minutes, adding more milk if potatoes are too dry.