Chop the mozzarella cheese and Salame Piemonte PGI into thin slices. Open the puff pastry sheet. Cut strips, from the center out, on both sides of the dough and leave a space in the center. Now fill with the salami and place the mozzarella over it. Braid the strips over the filling. Brush with egg yolk and cook in the oven for 30 minutes at 350 F, until golden brown.