Put the ingredients without the egg yolk in the bowl of the food processor and knead well with the dough hook. Add enough egg yolk until the crumbly dough separates from the side of the bowl and forms a firm, compact dough that is not too wet. Cover and let rest in the refrigerator for at least 1 hour.
Roll out on pasta roller about 20 times. Initially, the dough crumbles, then it becomes visibly more elastic.
Gradually fine the dough until it reaches level 4 or 5. Flour each time so that the dough does not stick and tear. Shape into tagliatelle, flour well. Cook in boiling salted water for a few minutes.