Step 1

Preheat oven to 180°C. Line 2 baking trays with baking paper.

Step 2

Place the butter, sugar and vanilla in the bowl of a stand mixer with the paddle attachment and beat until pale and fluffy. Beat in flour, custard powder and lemon juice until just combined.

Step 3

Using 1 tbs of mixture at a time, roll into balls, place 4cm apart on prepared trays, and gently press with a lightly floured fork. Bake, swapping trays halfway, for 14-16 minutes until faintly golden. Cool.

Step 4

For the filling, beat all ingredients together in a bowl to form a stiff icing. Spread over half the biscuits then sandwich with remaining biscuits. Dust with extra icing sugar to serve.