Preheat oven to 180°C. Spread the hazelnuts over a baking tray and cook in preheated oven for 10-12 min or until lightly toasted.
Rub the hazelnuts between a clean teat towel to remove as much skin as possible. Roughly chop the hazelnuts and set aside. Increase oven temperature to 200°C. Line 2 baking trays with non-stick baking paper.
Using electric beaters, beat butter and sugar until light and creamy Add egg and vanilla essence beating in thoroughly.
Using a metal spoon , fold in sifted flour and hazelnuts. Mix until well combined.
Shape level tablespoon of mixture into crescent shapes. Place on prepared trays. Bake 15 minutes or until lightly golden.
Set aside for 2-3 minutes on the trays to cool slightly. Place the extra icing sugar on a plate. Roll the biscuits gently in the icing sugar and transfer to a wire rack to cool completely.