Heat the oven to 190C/375F/Gas 5.
Beat the butter and the sugar together until smooth.
Stir in the flour to get a smooth paste. Turn on to a work surface and gently roll out until the paste is 1cm/½in thick.
Cut into rounds or fingers and place onto a baking tray. Sprinkle with caster sugar and chill in the fridge for 20 minutes.
Bake in the oven for 15-20 minutes, or until pale golden-brown. Set aside to cool on a wire rack.