Preheat oven to180°C.
Toast the hazelnuts in the oven for about 5 minutes to enhance their flavour, then let them cool down. Once cold, put them in a blender with the raw cane sugar.
Blend them with the pulse function not to overheat them, otherwise they will get too oily, until you get a fine and crumbly texture, just as cane sugar.
Place the blended hazelnuts with sugar into a bowl and mix it with the plain flour, the barley flour, the cocoa powder and a pinch of salt.
Pour the egg yolks in the centre and mix the dough with a fork.
Add the butter previously melted in a bain-marie, then pour in the milk and knead the dough with your hands until it is completely uniform and soft.
Line with parchment paper a baking tray.
Arrange the cookies on the baking tray either with a biscuit maker or simply by flattening with your hands small walnut size ball of dough.
Bake the cookies for about 10 minutes until the edges are golden brown, then remove them from the oven and let them cool for a few minutes before moving the cookies onto a wire rack to cool completely.
Serve the cookies during the coffee break dusted with plenty of icing sugar.