You begin by either steaming or boiling the potatoes in their jackets (Russets or Yukon golds would do well here) until perfectly tender. Drain them and run some cold water over them to cool them off slightly. Peel them as soon as they are cool enough to handle and cut them into chunks into a food mill.

Mill the potatoes into a dry pan over medium heat. With a wooden spoon, stir them and allow any water to evaporate. The potato puree will be rather stiff and hard to stir, but persist. And don't worry if some of the potato begins to stick to the bottom of the pan, as this is a sign that the potatoes are drying as they should and will anyway soon rectify itself.

Now that the potato flesh is perfectly dry, it is ready to absorb lots and lots of butter, which you will add to the potatoes a bit at a time. When I say a lot, I mean at least a stick or more (100 g) for 1 kilo (2 lbs.) of potatoes. Season liberally with salt. As you add successive bits of butter, the puree will soften and form a kind of a ball. Taste them--they should be well seasoned and have a wonderfully buttery flavor. If not, add more butter and/or salt. Finally, thin out the puree with some hot milk (whole milk, obviously!) or, if you are feeling particularly decadent, with some cream, until you reach the consistency you prefer. I like mashed potatoes rather soft, just thick enough to hold their shape.

Serve immediately. I like to place a dab of butter on top of the mashed potatoes, just for show.