Carefully wash the medium size potatoes;
In the meanwhile, bring a pot of water to a boil;
Add some coarse salt and the potatoes;
When the water returns to a boil, set the timer and cook for about 20 minutes. Test for the doneness with a fork;
For a very smooth and fluffy smashed potatoes, you have to smash them when they are still very hot. Take a thick bottom pot, or a copper one and smash the potato into one by one. Use a potato ricer with the medium plate: you will remove the peel without burning your fingers;
You have to be fast; if the potatoes cool down, they will get granulose. Heat up the milk;
Now, put the pot with the potatoes over medium-low heat and add the butter; stir well with a wooden spoon. Add the milk little by little until the desired consistency: the more milk you add, the softer mashed potatoes will get;
Stir to combine well, and remove form the heat; season with salt and pepper to taste (keep in mind that potatoes have a sweetish taste); go the extra mile: add a little grated nutmeg;
Serve very hot; if you want to prepare smashed potatoes in advance, add little hot milk and heat over medium heat or in the microwave.