Place the butter and sugar in a food processor (with chopping blade) and cream until pale. Once well mixed, add vanilla.
Sift all the fours together, then add the flour to processor and blend briefly, just until thoroughly combined.
Tip into a buttered Swiss-roll tin (23x33cm or 9x13"), using floured hands, press down so it is level all over.
You can use a spoon if preferred. Prick all over (do this carefully, so that you do not disturb the level surface)
Bake at 150C (fan forced) for 50-60 minutes. What you are looking for is a uniform pale golden colour all over. Do not allow it to become too dark.
Remove from oven and cut into squares or fingers in the tin, sprinkle the top with caster sugar. Leave to cool for 5 minutes or so then carefully lift out onto a wire rack, and allow it to cool completely. Store in air tight container.
Make at least 2 batches because there won't be enough to store after the family smells it cooking!!