250g unsalted butter, softened
200g soft icing sugar mixture, sifted
1 tsp vanilla extract
1½ cups plain flour
¼ cup cornflour
4 tsp lemon juice
Extra soft icing sugar mixture, to dust
Preheat oven to 150°C. Line 2 oven trays with baking paper. Put 200g of the butter and 60g of the icing sugar in the bowl of an electric mixer and beat on high, using paddle attachment, for 5 minutes or until pale. Add vanilla and beat. Sift in flours, then beat gently to combine.
Form dough into 32 pieces, each 2 heaped teaspoonfuls large. Arrange pieces 3cm apart on prepared trays. Flatten slightly with the base of a glass, then press with the back of a lightly floured fork. Bake for 20 minutes. Transfer to a wire rack to cool completely.
Meanwhile, put remaining butter and remaining icing sugar in the bowl of an electric mixer and whisk on high, using whisk attachment, for 5 minutes or until pale. Add lemon juice and whisk until combined. Use lemon icing to sandwich biscuits. Serve biscuits dusted with extra icing sugar.