Put 2 pounds whole unpeeled russet potatoes in a large saucepan and cover with cold water; season generously with salt. Bring to a simmer (do not boil) and cook until the potatoes are tender, about 45 minutes. Drain, then peel and return to the pan; add 1 cup hot milk and 1/2 to 1 stick room-temperature butter. Mash with a potato masher or fork (do not use a food processor). Season with salt and pepper.