Using a mixer, mix the hazelnut powder, brown sugar(1), whites (1), yolks, powdered sugar, salt, liquid vanilla and vanilla pod , split and scraped.
Then, beat the egg whites and fold in the brown sugar(2). Gently fold with a spatula the egg whites(2) into the previous mixture.
Add the sifted flour and the melted butter.
Bake in a ventilated oven at 170°C for about 15 minutes.