Preheat oven to 160 degrees celsius (fan-forced).
Line two baking trays with greaseproof paper.
Place the plain flour and cornflour into the Thermomix bowl and sift for 20 seconds, Speed 4. Set aside in a seperate bowl.
Place the butter, vanilla and icing sugar into the Thermomix bowl and mix for 40 seconds, Speed 3. Scrape down the sides of the bowl and repeat.
Add the reserved flour/cornflour mixture and mix for 20 seconds, Speed 3. Scrape down the sides of the bowl and mix for a further 10 seconds.Note: if the mixture is too sticky, add a little more flour and mix through. Roll teaspoonfuls of mixture into balls.Place onto the prepared trays, about 3cm apart.Use a fork dusted with cornflour to gently flatten. Bake for 15 minutes or until lightly golden and cooked through.
Allow to cool on the tray for 10 minutes before transferring to a wire rack to cool completely.
To make the filling, place the butter and icing sugar into a clean and dry Thermomix bowl. Mix for 30 seconds, Speed 4.
Add the passionfruit pulp and mix for 10 seconds, REVERSE, Speed 3.
Spread a small amount of filling onto the flat side of one of the biscuits. Sandwich with a similar sized biscuit.
Repeat until all of the biscuits have been used.