Dice the butter into cubes. Keep cold.
Place all of the ingredients in a food processor and pulse until a ball begins to form. Do not overwork in the food processor. Remove and finish kneading by hand until you have a firm ball of dough. Roll between 2 sheets of baking paper until 5mm thick.
Cut out the shapes you desire and bake in the oven for 15 minutes.
When golden brown on the edges and firm in the middle, sprinkle with the caster sugar whilst still hot and allow to cool.
«If you want to tidy up the appearance of your shortbread, cut them with a pastry cutter again when they come out of the oven. Then sprinkle with sugar and allow to cool.»