Peel the potatoes and cut them into 1-inch pieces. Submerge in cold water until you’re ready to cook (to prevent browning).
Place the potatoes in a large pot, cover with 1 inch of cold water, and bring to a boil. Reduce to a simmer and cook for 10-15 minutes until fork-tender.
While the potatoes are boiling, heat the milk and butter in a small saucepan until the butter melts and the milk steams. Do not let it boil. Cover to keep warm.
Drain the cooked potatoes, return them to the pot and set over low heat for 1 minute to evaporate excess steam. Mash the potatoes coarsely to break them up.