Vigourously knead the ingredients until gaining a smooth, soft dough. Leave in the fridge for 2 hours while you clarify the butter. Take the stick of butter and warm it in a bain-marie. Do not work the butter, let it melt until it forms a white patina on its surface, so remove it with a perforated spoon.

As the butter melts, the caseine sediments to the bottom and gives the butter a bright yellow colour. Now, using a spoon and a gauze-lined colander, gather the clarified butter (the liquid, bright yellow layer) and filter it. Try not to touch the caseine settled on the bottom.

Form the passatelli with a potato masher and boil them in generous salted water until they float on the surface, then drain and stir-fry them in a pan with a spoon of clarified butter and some basil leaves.