Preheat oven to 180°C. Grease 16 x 80ml capacity brioche or other metal moulds (see tip) with butter and place on an oven tray. Sift flour and icing sugar into a bowl. Stir in ground hazelnuts and chocolate chips until combined.
Lightly whisk eggwhites in a large bowl. Add butter and orange zest and whisk until combined. Add butter mixture to dry ingredients and stir with a whisk until just combined.
Spoon mixture into tins until ¾ full. Bake for 25-30 minutes
or until golden and a skewer comes out clean when inserted into cakes. Allow cakes to cool slightly before removing from moulds and transferring to a wire rack to cool.
Meanwhile, to make syrup, put juice and sugar in a small saucepan over a medium heat and stir until sugar dissolves. Bring to a simmer and simmer for about 10 minutes or until thickened to a syrup. Brush tops of cakes with syrup to serve.