Preheat oven to 180°C.
In a mixer, beat the butter,sugar and lemon rind until light and fluffy. Using a wooden spoon,stir in the flours until combined. Knead mix gently on a floured surface until smooth,and then cover in cling film and allow to rest for 30 minutes in the fridge.
Divide mixture into 36,roll into balls and place on a greased baking tray. Flatten the balls with the back of a fork. Bake for 12-16 minutes,or until crisp and light golden. Stand for 5 minutes,then transfer to a cooling rack.
To make filling, beat butter with a wooden spoon until pale and creamy. Add half the icing sugar and beat until well combined. Add the passionfruit pulp and the remaining icing sugar and beat until well combined and fluffy.
Spread passionfruit butter onto half the biscuits,using a palate knife or piping bag with a 1cm nozzle. Top with remaining biscuits,and dust with icing sugar.
Photography by William Meppem. Styling by Hannah Meppem. Food preparation by Kirsten Jenkins.