Method

• 1.
  Preheat oven to 180ºC. Grease 2 baking trays and line with baking paper.
• 2.
  Place butter in the bowl of a stand mixer fitted with the paddle attachment. Beat for 5 minutes until thick and pale. Add the icing sugar and custard powder, and beat until combined. Add flour and baking powder, and mix until just combined. Do not overwork the biscuit dough once you have added the flour or your biscuits will be tough.
• 3.
  Using a tablespoon, divide dough into 18 pieces. Use floured hands to roll into balls and place on prepared trays. Dust a fork with extra flour and press down on balls to flatten slightly.
• 4.
  Bake for 12-14 minutes (biscuits will be done when they move slightly when pushed with your finger, but are not coloured). Using a palette knife, carefully transfer biscuits to a wire rack and allow to cool completely before icing.
• 5.
  For the buttercream filling, place butter in the bowl of a stand mixer fitted with the paddle attachment. Beat until thick and pale. Add the icing sugar, custard powder and vanilla. Beat until thick and combined. Spoon into a piping bag fitted with a 2cm nozzle. Pipe the icing onto the flat side of a biscuit and top with a second biscuit. Repeat.

• 6.
  Biscuits will keep for 3-5 days in an airtight container.