Step 1

Preheat oven to 160C/140C fan-forced. Line two baking tray with baking paper.

Step 2

Using an electric mixer, beat butter, sugar and vanilla until fluffy. Sift flour and custard powder over butter mixture. Stir with a wooden spoon until soft dough forms.

Step 3

Roll dough into 2cm balls. Place on prepared trays, 4cm apart, to allow room for spreading. Using a fork dipped in flour, lightly flatten each ball until 1cm thick. Bake for 20 minutes or until light golden. Cool on tray for 10 minutes. Transfer to a wire rack to cool completely.

Step 4

Meanwhile, make Filling. Using an electric mixer, beat butter and sugar in a bowl until light and fluffy. Divide among 4 bowls. Tint 1 portion green with green colouring and stir in lime rind. Tint another portion yellow with yellow colouring and stir in lemon rind. Tint 1 portion pink with pink colouring and stir in grapefruit rind. Tint remaining portion orange with yellow and red colouring, and stir in clementine rind.

Step 5

Spread 1 teaspoon of the various fillings among half the biscuits. Sandwich with remaining biscuits. Serve.