Make a well in the center of the crumbs. With a fork, lightly beat the salt and egg, then pour this mixture into the well. Draw in the flour gradually and blend with your fingertips, then squeeze the dough rapidly between your hands. Do not knead. When the dough is no longer sticky, press it into a ball and flour lightly.
Wrap the dough in a plastic bag to prevent it drying out. Refrigerate for at least 2 hours. The dough can be kept in the refrigerator for several days.
