Preheat oven to 160°C (140°C fan forced). Line three baking trays with baking paper.
Remove pulp from passionfruit, place pulp into a sieve and press down with the back of a spoon. Put a few of the seeds back in if you like. Reserve 1 tablespoon of passionfruit juice for the passionfruit butter cream.
Beat the butter, vanilla and sifted icing sugar with an electric mixer until pale. Stir in combined sifted flours in two batches then stir in passionfruit pulp.
With lightly floured hands, roll two level teaspoons of mixture into balls and place on oven tray about 3cm apart. Dip a fork into a little extra flour, press biscuits lightly.
Bake for 15 minutes or until biscuits are a pale straw colour. Leave the biscuits on the trays for 5 minutes, then transfer to wire racks to cool.
To make the passionfruit butter cream, beat the butter and sifted icing sugar in a small bowl with an electric mixer until pale and fluffy. Beat in the reserved passionfruit juice.
Sandwich two biscuits together with a teaspoon of the passionfruit butter cream. Repeat with remaining biscuits and dust with a little extra sifted icing sugar, if desired.
