Special equipment: food mill

1. Cook the potatoes: In a large pot, add the potatoes and cover amply with cold water. Bring the water up to a boil and reduce the heat so it simmers. Add a generous pinch of salt to the water and allow the potatoes to cook until tender when pierced with the tip of a knife, 20 to 25 minutes. Drain the potatoes in a colander and, while still hot, put them through a food mill.
2. Mash the potatoes: Return the empty pot to the heat and add the milk. Bring the milk to a simmer and gingerly add the potatoes back into the pot. Season with salt and pepper and gently mix in the butter and sour cream. Do not over mix – over mixing makes gummy potatoes. Taste for seasoning. Remove from the heat.
3. Finish the potatoes: When ready to serve, use a whisk (or an electric mixer fitted with the whisk attachment) to whip the heavy cream in a medium bowl until fairly firm. With a rubber spatula, gently fold the whipped cream and the Parmesan into the mashed potatoes. Taste for seasoning. Serve immediately.