Combine flour, sugar, cocoa powder and egg yolks in a large bowl.

Add the egg yolks one by one and mix. Help with your hands to obtain a more uniform and soft dough.

Add the melted butter to the dough. Mix well until the dough is homogeneous.

Roll out the dough using a rolling pin, to obtain a layer 1/3 inch thick.

Cut the cookies with the shape of your choice using a cookie cutter.

Lay the cookies on a baking sheet. Top with some sugar.

Bake in the oven at 320 F for about 20 minutes or until slightly brown

Another easy way to obtain perfect cookies is to shape the dough as long and thick logs. Refrigerate for a while to harden the dough and then just simply cut the dough in 1/2 inch slices