Preheat oven to 160 degrees celsius.
Line two baking trays with greaseproof paper.
Measure the plain flour, pure icing sugar and cornflour into the Thermomix bowl and sift on Speed 4 for 15 seconds to combine.
Place the flour mixture into a separate bowl and set aside.
Place the room temperature butter and lemon rind in the Thermomix bowl.
Beat on Speed 4 for approximately 1 minute or until the mixture is pale, fluffy and smooth.
Add the flour mixture and combine on Speed 1, slowly increasing to Speed 4 until smooth and completely combined (if your mixture is too sticky, add a little more flour).
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, combine the butter and icing sugar on Speed 4 until pale and smooth.
Add the passionfruit and lemon juice and mix for 1 minute or until smooth and fluffy.
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.
Store in an airtight container for 4-5 days.