With a clean sponge, clean the potatoes by rubbing them slightly under running water.
Salt the potatoes, wrap them in aluminum foil and bake in a preheated oven at 140oC until they soften for about 90 minutes (if you pierce them with a small knife there should be no resistance).
Heat the milk in a saucepan on medium heat and keep it warm.
Unwrap the potatoes, let them cool a bit and peel them.
Grind them in the food mill with the fine sieve and put them in a pot.
Place the pot on medium heat and stir for 2-3 minutes with a ladle. Add the butter little by little, add salt and mix, making sure to homogenize the mixture before adding the next piece.
Add the milk slowly while stirring, until it is also incorporated in the mixture.
Serve the mashed potatoes right away or keep it warm.
* Mashed potatoes offer you the chance to experiment with various flavors. Add basil pesto and create scented mashed potato with basil flavor. The same can be done with other vegetables such as celery root or beetroot.
* If you want, you can keep the peels from peeling the potatoes and fry them at a low temperature of 165oC in sunflower oil like crisps. It is a very tasty snack.
* If you do not consume the mashed potatoes directly, place some wrap on its surface so that it does not get dry.