Sift in the flour, cocoa, and salt; mix to combine, kneading with your hands if it is too difficult to stir.

Cover with plastic and refrigerate until using, or make the cookies right away.

Beat the egg whites until frothy. Shape the dough into walnut-sized pieces, and dip each ball into the beaten egg white. Roll with chopped nuts.

Press the cookies onto non-stick or parchment lined baking pans, making a deep indentation in the middle with your thumb. Bake in a 350 degree oven for 8-10 minutes or until the nuts are lightly golden and the cookie centres look dry (they will have a wet unbaked look if they aren't ready).

When the cookies are done, using the back of a spoon, re-enforce the indentations in the middle of each cookie while they are still warm (they will have risen up in the oven a little bit). Cool completely on wire racks.

Spoon some chocolate hazelnut spread into a prepared piping bag, snip of the tip, and pipe some of it into the centre of each cookie to fill it up (if you do this while the cookies are warm, the filling will melt and you will have to let it set again before you can serve them).

Melt a bit of dark or milk chocolate melting wafers in the microwave or in a double boiler. Spoon the chocolate into a plastic squeeze bottle, piping bag, or freezer bag with the tip/corner snipped off. Drizzle the tops of the cookies. Allow the chocolate to set before serving.