Sieve flour, add salt and mix the butter with egg with a dough scraper, then the dough does not get too hot through your hands.
Then pour the dough onto a marble slab (if you have one).
Mix the butter well with the palms by the flour. Rubbing away from you. The marble slab is handy for this.
Continue and mix with milk until a nice dough is created. Do not go too far, because then the dough becomes too elastic, that is
again not good, because then it pulls back into the form.
Packaged in foil and put away in the refrigerator, preferably a few hours in advance.