Preheat the oven to 160C. Line two baking trays with non-stick baking paper. Set aside.
Using an electric mixer or freestanding mixer, cream the butter, vanilla extract and icing sugar until light and fluffy. Sift flours over butter mixture. Beat on low speed until a soft dough forms.
Roll heaped teaspoonfuls of mixture into small balls. Place on trays. Using a fork dipped in flour, lightly flatten each biscuit until 1cm thick. Bake for 15 minutes or until firm. Cool on trays for 10 minutes. Transfer to a wire rack to cool completely.
To make the passionfruit filling, using an electric mixer or freestanding mixer, beat the butter until light and fluffy. Stir in passionfruit pulp and icing sugar. Add a bit of food colouring for a nice yellow tinge. Place in the fridge to chill for 15 minutes.
Using a spatula or piping bag, spread/pipe one biscuit with 1 teaspoon of filling. Top with another biscuit. Repeat with all remaining biscuits and filling.
Makes about 30. They last for ages in an airtight container.