This recipe is the traditional Tuscan mashed potatoes. Olive oil is obviously the choice to add to the potatoes as people use butter very seldom or in very little quantities (butter would be used more in the north part of Italy). —Maria Teresa Jorge
Wash, peel and cut the potatoes in pieces all the same size. Don't wash the potatoes after you cut them so they keep the starch.
Put them in a pan with the cold milk and cook over very low heat (don't put a lid on as the milk easily comes up and out of the pan). Check for doneness by inserting the blade of a sharp knife through the potatoes.
Shave the parmesan cheese.
Drain the potatoes, reserving the milk and keeping it hot. Before the potatoes cool, mash them through a potato ricer or a hand held food mill (DO NOT process them or they will become gluey). Put them in a heat proof bowl or a pan, away from the heat and stir vigourously the olive oil into the potatoes with a wooden spoon. Add the hot milk in a stream until you have the right consistency (go slowly with the milk, it's easier to add a little more if needed then ending up with a very liquid purée).
Season with salt, freshly ground WHITE pepper, the parmesan cheese and pinch of freshly grated nutmeg.
Keep warm in a bain-marie (don't put the pan directly over heat). Serve as quickly as possible, with a drizzle of olive oil and some grated nutmeg on top.