Place potatoes in a medium pot and cover with cold water.
Bring to a boil, heat to a simmer. Add a generous pinch of salt and continue to simmer until potatoes are fork tender, about 20 minutes. When potatoes are done, drain and return potatoes to pot to dry slightly. Run potatoes through food mill or potato ricer into pot. Heat milk in saucepan. Add hot milk to potatoes, over heat, until smooth. Add butter and heat until finely textured and fluffy.