In the bowl of a stand mixer, beat butter until smooth (1 min).Add sugars and beat until fluffy and light in color (5 min).
Scrape down the sides of the bowl and beat in the egg and vanilla until well combined.
Mix in the hazelnut meal just until combined.In another bowl whisk together flour with cacao, baking powder and salt.Slowly mix in the flour mixture until just combined.
Turn the dough out onto plastic wrap, and shape into a disk.Refrigerate for at least 1 hour.
Preheat oven to 180C degrees.Roll out dough into 4mm height on a lightly floured surface.
Cut out an even number of cookies with a cookie cutter.
Use a smaller, decorative cutter to cut a shape out of the center of half of the cookies.
For perfect cookies, I suggest refrigerating the cut out cookies for 15 minutes.
Bake for 8 minutes, until they are lightly browned on the bottom.
Let cool down a few minutes on baking tray then transfer to a cooling rack to cool completely.