Grill the hazelnuts around 10 mins. Let cool down few minutes. Then rub them between the two hands or in a kitchen towel. Personally I like to keep some of the brown peel.
In a food processor put the grilled hazel nuts, the granulated sugar and the cacao. Give them few pulses. Until you have some powder and some big chunk of hazelnuts
Beat the egg whites into soft peaks . Fold in the icing sugar and the hazelnuts
Spoon them on a baking tray lined with parchment paper. Bake 10 mins in s preheated oven 180C
Out of the oven. Let cool around 1 hr