Preheat the oven to 170ºC and line. Line a baking tray with baking paper.

In a stand mixer or using a hand mixer cream the butter, icing mixture and vanilla until pale and fluffy. This should take 5 minutes.

Sift the plain flour and custard powder over the butter mixture.

Using a spatula, fold the flour and custard powder through the butter mixture.

Using your hands (lightly floured) roll teaspoons of the mixture between your fingers and palms. In my view, smaller is better. Place the balls on the baking tray around 5 cm apart.

Using your three middle fingers press down each ball to form a disc.

Using the back of a fork, dipped in flour, press the tip (lengthways) on the top of each disk to form three/form lines (depressions). Thinner biscuits are easier to eat (don’t forget one melting moment is 2 biscuits sandwiched together. If the biscuits are too big it’s hard to get your mouth around). The biscuits will puff up a little as they bake so don’t be afraid to use some force when pressing the balls into discs.

Bake the biscuits for about 15 minutes. Cool the biscuits on the baking tray.

While the biscuits are cooling make the butter filling.

Place all the ingredients into a bowl and cream them together until light and fluffy. This should take about 3-4 minutes.

You can fill the biscuits using a piping bag and nozzle, an offset spatula or butter knife. You’ll get the best looking results from piping the butter filling.

Pipe the butter filling onto only half of the biscuits.

Top each buttered biscuit with an unbuttered biscuit and lightly press together so that the butter filling spreads to the edges of the biscuits.