Scrub the potatoes (shown to left are Ratte's from Union Square Market) Do not peel the potatoes. Cook them in their skins covered by at least 1 inch of water. For each liter of water add 10 grams of salt. Simmer uncovered over moderate heat for 20-30 minutes or until a knife can easily be inserted and removed. As soon as the potatoes are done remove and drain. Do not allow them to sit in the water.

Meanwhile, bring the milk just to a boil in a medium sized saucepan and set aside.

Once potatoes are cool enough to handle (but still hot), peel them and cut into manageable pieces. You can discard the skin or use them in another dish. Then pass the potatoes through the grid of a food mill (or use a potato ricer) passing them into a large heavy bottomed saucepan

Discard the skin after it has been peeled away. Place the pan over low heat and using a wooden spatula stir the potatoes to dry them out (approximately 4-5 minutes).

Begin adding 3/4 of the butter, little by little vigorously stirring until the butter is incorporated. This should be done in a similar manner as one prepares any butter emulsion (starting off with a very small amount of butter to start the emulsion).

.Slowly add the milk in a thin stream (a little at a time) till the desired consistency is reached. You may only need a very small amount of the milk, depending on the potatoes used, amount of butter used, and personal taste. Stir vigorously till all the milk is incorporated.

Then stir the puree with a whisk to incorporate air and make the puree fluffy.

Pass the puree through a fine drum sieve to further lighten and smooth the dish. This can be repeated 2 or 3 times for to make the puree silky smooth.

Taste for seasoning. If not using immediately, place in the top of a double boiler over simmering water. Whisk occasionally to keep smooth. The puree can be further adjusted with hot milk or butter before serving.