Makes:

Method:

1. preheat the oven to 160°C
2. put the icing sugar, plain flour and cornflour into the bowl of a food processor fitted with the double-bladed knife and give them a quick blitz before adding the butter along with the vanilla seeds you've scraped out of a vanilla pod. (Easiest way to do this is by cutting the vanilla pod in half across, and then splitting each short half lengthwise and prising out the seeds with the point and edge of a sharp knife. Nigella's tip - don't even think of throwing the deseeded bits of vanilla pod away: stash them in a jar of caster to use next time a recipe requires vanilla sugar.)
3. process again until the soft mixture coheres and begins to form a ball, loosely clumping around the blade. Turn this out on to a Swiss roll tin and press to form an even (or as even as you can make it) layer, using fingers or the back of a spoon, or both.
4. using the tip of a sharp knife, cut the pressed-out shortbread into fingers. Make two incisions lengthways - ie to form three layers - and then make ten cuts down - so that you end up with eleven fingers per layer.
5. slide the Swiss roll tin (baking tray) into the oven and bake for about 20-25 minutes, by which time the shortbread will be pale still, but not doughy. Expect a little goldenness around the edges, but shortbread should be not crisp but melting.
6. Remove the tin from the oven and let cool for 10 minutes or so, before removing, with a palette knife and your fingers, to a wire rack. Sprinkle with sugar and leave them to cool completely before storing in a tin.