This is one of the easiest shortbread recipes I've ever come across.

9 oz plain flour,
9 oz self-raising flour,
9 oz cornflour,
9 oz castor sugar,
2 250gm packs butter

Method
Sift dry ingredients into a large bowl.
Melt butter gently in a saucepan.
(Be careful at this stage; "chip pan fires" can happen with hot butter!) Pour melted butter into the dry ingredients and mix thoroughly.

Divide the mixture into two and spread evenly into two baking trays (approx 16" x 10"). Prick the shortbread with a fork at intervals - create a pattern, if you like. Place the baking trays into a moderate oven (I use a fan oven which I heat to 150ºC) and bake until golden brown.

Take out of the oven and cut into portions, dust with castor sugar and allow to cool completely before storing in an airtight container.