Place the peeled and cubed potatoes in a medium pan with about 3 cups of water. Bring to a boil and cook until fork-tender, then drain thoroughly.

Transfer the hot potatoes to a large bowl. Add milk or cream, butter, salt, and pepper. Using an electric mixer, beat on high speed until smooth, then continue beating for 3 minutes to incorporate air and achieve a fluffy texture.

Taste and adjust seasoning. Serve immediately while hot and fluffy, or keep warm over simmering water if needed.