In a small bowl, dissolve the instant coffee in hot water completely and set aside.

Cream the butter and icing sugar in an electric mixer. Add the ground hazelnut to the mixture, making sure to mix well. Fold in the plain flour and bicabornate of soda. Then add in the instant coffee mix and cream until a cookie dough forms.

Divide into equal portions, make into round shaped cookies and flatten onto a greased baking tray. Brush the cookies with some egg yolk and decorate with hazelnut halves.

Bake at 180C for about 20 minutes or until golden brown.