1.Preheat the oven to moderately slow, 160°C (140°C fan- forced). Grease the oven trays.
2.Beat butter, vanilla and 1/3 cup of the icing sugar, sifted, in a small bowl with an electric mixer until light and fluffy. Add milk, beat until combined.
3.Add sifted plain flour and cornflour; beat on low speed until combined.
4.Refrigerate biscuit dough for about 10 minutes or until firm enough to roll. Roll the dough in baking paper into a 4cm-diameter log (about 30cm long). Refrigerate dough for 1 hour.
5.Cut the dough into 4mm slices. Place slices on prepared trays about 3cm apart. Bake for about 10 minutes or until just golden. Stand the biscuits on trays for 3 minutes; transfer to wire racks to cool slightly. While still warm, dust the biscuits liberally with the remaining icing sugar. Cool completely on wire rocks.
Store in an airtight container at room temperature for up to 1 week.Note