Cut peeled potatoes into halves or quarters if very large. Place in a pot and cover with cold water. Bring to a boil and boil partially covered for 20-25 min or until potatoes are tender when you poke them with a fork.
Drain well, and transfer to bowl of your stand mixer. Mash the potatoes a little by hand to break them up, then attach whisk to the stand mixer and whisk on low speed for 30 seconds, then increase speed to medium and slowly drizzle in the hot milk.
Once milk is combined, add the butter, one cube at a time while mixer is still running. Wait a few seconds between each addition. Once all butter is added, add in the salt and pepper.