Preheat the oven to 170C. Grease and line a baking tray with baking paper.
Beat the butter, vanilla and icing sugar in a large bowl until fluffy. Sift together the plain flour and cornflour, then add in two batches, folding through.
Roll 2 teaspoons of mixture to form balls, put them 3 cm apart on the tray and flatten slightly with a fork.
If the dough is sticky, lightly flour you hands.
Bake for 12-15 minutes, or until the biscuits are a pale golden colour.
Cool slightly on the tray before transferring to a wire rack to cool.
Blend the butter, icing sugar and passion fruit juice in a small bowl for the cream.
Sandwich 2 biscuits together with icing in between. Dust with icing sugar. Store in an airtight container.