To cook the potatoes :
To finish the purée:
Put the washed potatoes (don’t peel them) into a large saucepan and cover with cold water.
Boil on a low to medium heat until soft, check with a small sharp knife if all potatoes are equally cooked.
Drain and leave to cool for a while until you can manage to peel them.
Now press the potatoes through a potato ricer or sieve, or mash them with a potato masher.
Put the mashed potatoes back into the sauce pan and gradually add butter and the milk stirring continuously. Season, taste and add more salt if needed. If the purée is too firm stir in more milk. Serve warm.