These are an absolute classic in Canary island cuisine.
Wash the potatoes and set aside.
Fill a pan with water and “a lot” of salt. To get the required amount of salt add and let dissolve in boiling water until a potato which is put into the pan no longer sinks to the bottom but floats.
Boil the potatoes until cooked.
Then pour off the water and place back on the stove. Let any residue water evaporate, while the pot is gently shaken until the remaining salt crystallises on the skin giving a “wrinkly” appearance.