Line 2 baking sheets with baking parchment.Beat the butter and icing sugar together with an electric whisk until pale and fluffy, add the vanilla extract and orange zest and beat again until combined.
Mix the flour and cornmeal together and add to the butter mixture, beat gently, then bring the mixture together with your hands into a stiff dough, it will be quite crumbly, knead very gently for a few seconds just enough to form it into a smooth ball.
Roll out on a lightly floured surface to about 5mm thick and cut out biscuits using a 6cm plain round cutter (or cutter of your choice), place on the baking sheets and chill in the fridge for 1 hour, or the freezer for 20-30 minutes.
Meanwhile, preheat the oven to 180°C/350°F/gas mark 4.Bake the biscuits in batches, one tray at a time, for 10-15 minutes until golden. As soon as they come out of the oven, sprinkle with a little sugar then transfer to a wire rack to cool.