Cream butter and icing sugar until light and fluffy.
Add vanilla essence, then sift through custard powder and baking mix and stir to combine.
Roll into 48 small balls and place on a tray lined with baking paper. Gently flatten each ball with a fork.
Bake for 10 minutes, remove from oven and allow to cool completely.
Blend butter, custard powder and icing sugar together until a smooth paste is reached. Mix through passionfruit pulp, without over stirring. Refrigerate filling until required.
When the biscuits are completely cool, sandwich together with the filling.