Here it is the secret recipe!
First, chuck 8 to 8 and a half ounces of plain flour into the food processor, with 4 to 4 and a half ounces of cornflour. Blitz for a few seconds to mix. Then add 4 to 4 and a half ounces of caster sugar and 8 ounces of cubed butter. Pulse and then blitz until well mushed together. Carefully remove blade from mass. Take out dough, and divide into 2 equal parts. Knead each gently until smooth.
Press each half into a lightly greased 7 inch sandwich tin. I use the back of a spoon to smooth surface evenly. Using the back of a fork, press around the outer edge (see picture). Prick all over with a fork. Chill out in fridge - (the shortbread that is) for a minimum of one hour.
Heat oven to 160 degrees. Place shortbread on top shelf, and bake for between 35 and 45 minutes, checking half time and if necessary change places if over browning. When shortbread is golden brown remove from oven and using a sharp knife cut into eighth's. Leave to cool in tin.
When cool tip out place in biscuit tin and dust with caster sugar.
Be sure to sniff contents every time you lift the lid.