Add the potato chunks to a pot and add just enough water just to cover them.
Cook over medium heat, uncovered, for 25-30 min. They should be soft and easily pierced with a fork.
Turn the heat off, and add butter, salt, and pepper.
Mix until you get the consistency you want. Be gentle, and don’t over-mix. The more you mix, the smaller the potato chunks will be, and the thicker the cooking liquid will become.