Mix flour, salt, sugar and yeast, add milk and egg, mix until smooth and knead the dough, gradually adding softened butter. (I do it in a bread maker.) The finished dough should be smooth, soft, shiny and almost not sticky. Put the dough in a bowl, tighten with a film and leave to come up for an hour and a half in a warm place. The dough should increase in volume by about half. Roll out the dough and put it in the refrigerator overnight.