Preheat the oven to 180°C (fan).
In a large mixing bowl, cream together the butter and sugar with a spatula or wooden spoon.
Add in the flour, cornflour and the zest of the orange and work into the mix by rubbing between your fingertips until a crumb consistency is achieved, then bringing together into a dough.
Turn the dough out, flatten into a rectangle shape, wrap in cling film and place in the freezer for at least 15 minutes.
While the dough is chilling, make the filling by melting the chocolate in the microwave in 30 second blasts, stirring in intervals. When it is completely melted, combine with 75g of fresh juice squeezed from the orange. Set to one side.
Once the dough is chilled, remove the cling film and roll the dough out to a 5mm thickness on a lightly floured surface. Cut out rounds and place them on the lined baking tray.
Bring the offcuts together, roll out and continue to cut rounds until all of the dough has been used up.
Cut stars out of the centres of half of the rounds, placing them on the baking tray in between the rounds.
Bake for 12 minutes, then allow the biscuits to cool completely on the tray.
Once cooled, use a spoon to spread the chocolate filling on the base biscuits then sandwich with the star-centre top biscuits. Dust with icing sugar and serve.