• Preheat oven to 180 degrees celsius (fan-forced) and line two baking trays with baking paper.
• Sift the icing sugar into a bowl and add the butter and vanilla essence.
• Beat until smooth and creamy.
• Sift into the bowl the self-raising flour, plain flour and custard powder, then stir well.
• Roll the yoyo mixture into teaspoonful sized balls and place them 5cm apart on the prepared trays.
• Lightly press the tops of the balls with a fork and place into the oven to bake for 10-12 minutes or until lightly golden.
• Allow for 5 minutes on the trays before moving to a wire rack to cool completely.

Thermomix Instructions

• Preheat oven to 180 degrees celsius (fan-forced) and line two baking trays with baking paper.
• Add the butter, icing sugar and vanilla extract to the Thermomix bowl and mix for 30 seconds, speed 2. Scrape down the sides of the bowl and mix for a further 30 seconds, speed 3 or until pale and creamy.
• Add the self-raising flour, flour and custard powder and mix for 10 seconds, speed 4.
• Use the kneading function to mix for 40 seconds.
• Roll the yoyo mixture into teaspoonful sized balls and place them 5cm apart on the prepared trays.
• Lightly press the tops of the balls with a fork and place into the oven to bake for 10-12 minutes or until lightly golden.
• Allow for 5 minutes on the trays before moving to a wire rack to cool completely.

To Make the Filling

• Make the filling by beating the butter, vanilla essence and lemon juice until smooth and creamy. Slowly add the sifted icing sugar and continue to beat.
• When the mixture is smooth, divide it equally between two bowls.
• Add one drop of pink food colouring to one bowl and one drop of blue food colouring to the other.
• Beat each bowl until smooth and evenly coloured.
• Spread a small amount of filling onto the base of one biscuit and sandwich with a second. Repeat until all of the biscuits have been used.