Pre heat the oven to 160'C
Line a baking tray with baking parchment.
Sieve the icing sugar, cornflour and the flour (keep them separate).
In a mixer, beat together the butter and the icing sugar until light and fluffy in texture. Once the icing sugar and the butter is at this stage, add the flour and cornflour (a small spoon at a time) and fold gently, using a spatula.
When the mixture has formed a smooth dough, split it evenly between two bowls.
Sieve the cocoa powder into one of the bowls and gently fold.
When the mixtures are ready, place them into two separate piping bags with piping nozzles and pipe 2cm sized stars onto the baking sheet, ensuring there are gaps in between to prevent them from sticking together.
Bake the biscuits for 8 minutes until just cooked.
Remove from the oven and allow to cool.
Cut the vanilla pod in half and scrape the seeds. Sieve the icing sugar. Place the vanilla, icing sugar and the butter into machine and beat together until the mixture is light and creamy. Place the mixture into a piping bag.
Arrange the biscuits in pairs of the same size ready to be filled.
Turn the biscuits flat side up. Pipe a pea sized amount directly into the middle of the flat sides. Gently sandwich the biscuits together.
«When the biscuits come out of the oven they will feel soft. Do not bake them any longer or they will toughen up.»