Beat together the butter and sugar for about 5 minutes until very light and fluffy. While it’s beating add the vanilla, salt and baking soda.

Add the egg whites and beat for a few more minutes. Sift in the black cocoa and flour and beat to just combine. Wrap the dough in plastic wrap and set in the fridge for a couple of hours.

Preheat the oven to 350 F. Line two cookie sheets with parchment paper.

Flour the counter and roll out the dough to about a quarter of an inch (the thinner the crispier they will be) and use cookie cutters to cut out shapes. Dust the cookie cutters in flour so the dough doesn’t stick to them.

Set the cookies on the trays and bake them for 10 minutes.

Once all the cookies are baked, lower the heat to 225 F and bake for another 20 minutes (this will dry them out more and make them crispy).