Using electric beaters, soften the butter in a bowl.
Add the caster sugar and vanilla and combine, using the beaters, until the ingredients are light and fluffy.
Sift the plain flour and the cornflour into the creamed butter mixture, then combine using a metal spoon.
Turn the mixture out onto a lightly floured surface and gently knead until smooth.
Roll out the dough with a rolling pin covered in flour to about 1 cm in thickness, then press out shapes using biscuit cutters of choice.
Place the shortbread onto trays covered with baking paper, and sprinkle with a little extra caster sugar if desired.
Bake at 160C for 25 minutes.
