This is how to make mashed potatoes with four ingredients.
Boil potatoes in an 8-quart pot of salted water until tender, about 25 minutes. Drain potatoes and set aside to let cool slightly. Meanwhile, bring milk to a boil in a 1-quart saucepan; remove from heat, cover, and set aside.
Peel potatoes and pass them through a food mill into a saucepan over medium low heat. Using a rubber spatula, turn potatoes frequently until they take on a drier, fluffier consistency, 2-3 minutes. Reduce heat to low. Working in batches, vigorously stir in the butter until mixture is creamy. Whisk in warmed milk, season potatoes with salt, and transfer them to a warm serving bowl.