Place potatoes in pot, cover with cold water. Season with salt, bring to a boil. Reduce to a gentle simmer for ~ 10 to 12m
Drain and return to pot. Let it sit over low heat for 1 to 2m to evaporate moisture.
Mash potatoes
Warm milk over low heat until hot but not boiling. Gradually fold warm milk into potatoes, stirring gently to combine.
Fold diced butter into potato/milk mixture.
Season with salt and pepper.
Don't overmix!