In a stand mixer or using hand-held beaters, beat butter and sugar until pale and creamy. Add flour, cornflour and vanilla, and beat until smooth. Turn out onto a large strip of cling film and bring together into a disc. Wrap in the cling film and refrigerate for 30 minutes to chill.
Preheat oven to 160C/140C. Line 2 large oven trays with baking paper. Remove dough from fridge and roll into 28 small even balls. Place on baking trays a few centimetres apart, and use a fork to gently flatten.
Bake for 15 minutes, then remove from oven and allow to cool on the tray.
To make filling, sift icing sugar into a bowl and add butter and vanilla. Beat for 3 minutes until very smooth and creamy. Add cream and continue beating until thick and smooth. Transfer to a piping bag with a star tip.
Make the passionfruit glaze by sifting icing sugar into a small bowl. Strain passionfruit pulp through a sieve to separate seeds from liquid. Add enough liquid to the icing sugar to form a spreadable glaze. Add back in a few of the seeds.
Pipe filling onto the flat side of half the biscuits. Top with remaining biscuits. Spoon a little of the passionfruit glaze over each biscuit and allow to set.
