Cream together margarine, sugar and vanilla sugar until pale.
Add flour, corn starch and cocoa powder. Then mix until everything is combined well. You should now be able to form a lump of dough.
Place this in the fridge for at least 30 minutes.
Meanwhile dust a flat surface with flour lightly. Also dust your rolling pin and start rolling out the dough until you receive a thickness of about 0.4 mm. Cut out stars (or your preferred shape).
Place them on a baking tray lined with parchment paper and leave them to chill in the fridge or a cool place for another 30 minutes.
Preheat the oven to 180°C.
Bake the biscuits for about 8 minutes. Then set aside to cool.
Melt the chocolate in the microwave or in a water bath.
Use a piping bag or spoon to drizzle the chocolate on top of the shortbread!