Simmer the potatoes starting in cold water , do not boil, cook until tender to the knife.
While cooking the potatoes, bring to a boil the milk and butter and set aside.
Strain the cooked potatoes in colander or pastry rack and let it dry steam for 3 minutes (removing as much of water as possible).
Pass the potatoes thru a food mill (or a ricer but never in a food processor) into a stand mixer bowl.
With the paddle, incorporate the milk and butter mix, add 3/4 of the seasonings.
Give a strong whip (with the paddle) to make the purée fluffy.
Taste and add more seasoning if necessary.
Serve hot (can be held in warm oven, covered with aluminum foil and a touch of butter on top of the mashed potatoes).