2 Tbsp finely chopped pistachios
2 Tbsp raw sugar
250g unsalted butter, chopped, softened, plus extra 70g
½ cup icing sugar mixture, plus extra 1½ cups, and extra, to dust
1 tsp vanilla essence
2 cups plain flour
½ cup custard powder
Finely grated zest of 1 lemon
2 Tbsp lemon juice
Preheat oven to 160°C fan-forced (180°C conventional). Line 2 oven trays with baking paper. Combine pistachios and raw sugar in a small bowl. Set aside.
Put butter, icing sugar and vanilla in a large bowl and beat on high, using an electric hand mixer, for 2 minutes or until light and fluffy. Sift in flour, custard powder and beat on low until just combined.
With lightly floured hands, roll dough into Tbsp-sized balls (28 in total). Arrange on prepared trays 3cm apart. Flatten slightly with a lightly floured fork. Gently press forked tops into pistachio mixture to coat. Return to trays. Bake for 14 minutes or until slightly golden. Set aside on trays to cool completely.
To make filling, put extra butter in medium bowl. Sift in extra icing sugar. Add zest and juice. Beat on low, using an electric hand mixer, until combined then increase to high. Beat until pale and fluffy.
Sandwich 2 biscuits with a little of the filling. Repeat for remaining biscuits. Dust with extra icing sugar. Serve. Sandwiched biscuits will keep in an airtight container for 2–3 days (will soften slightly).