Pre-heat the oven to 150ºC (302℉).
Grease a small, round pan. I used an 18cm (7") spring-form, but you could pretty much use any size (and then adjust the baking time accordingly).
Beat the butter and sugar together until light and fluffy.
Combine the flours and stir into the butter/sugar, mixing until a dough pulls together. Scrape the last bits together with your hands.
Press the dough into the prepared pan and push it outwards with your fingers until it covers the whole pan (just the bottom, it doesn't go up the sides).
Take the back of a spoon and smooth the top until it is even.
Decorate by pricking the dough all over with a fork.
Score lines into the dough (almost all the way through), as this will help cut the shortbread later.
Sprinkle a little sugar over the top.
Bake for around 30-35 minutes, just until the edges are browning but the rest still looks pale.
Cool for ten minutes or so. If using a springform pan, remove the edges.
Cut through the scores you made before baking to give you wedges, but leave the shortbread where it is and don't move it until it is completely cooled. Enjoy!