According to the recipe they store really well and taste better if freshly iced. So they suggest only icing them as you need them and storing the rest in an airtight container.
180g softened unsalted butter
1 teaspoon grated lemon zest
2/3 cup pure icing sugar
pulp of three passionfruit
100g cornflour, sifted
180g self raising flour, sifted
50g unsalted butter
1 cup pure icing sugar
pulp of 2 passionfruit
Briefly cream butter, zest and icing sugar in a food processor (be careful not to over process). Mix in passionfruit pulp, cornflour and flour. Scrape mixture into a bowl and chill for 20 minutes. Meanwhile, preheat oven to 220 degrees. Pipe rounds or fingers of batter onto baking trays lined with baking paper and bake until golden brown, 5-8 minutes. Cool on a wire rack before icing.
To make the icing, melt butter in a bowl over simmering water. Add passionfruit pulp to butter and then stir in icing sugar. Beat hard for 1-2 minutes until the icing is really shiny. Dip each biscuit into icing and place on a wire rack with baking paper underneath to catch the drips.