Beat the butter and sugar together in a bowl until smooth. Sift in the flour and fold until well integrated and the mixture comes together in a ball. Turn out onto a lightly floured work surface and roll out to 1cm thick. Cut into fingers and place onto a lightly greased baking tray.
Sprinkle the fingers with caster sugar, if desired, and put into fridge for 20 minutes. Remove from the fridge just prior to baking.
Bake in oven for 15 to 20 minutes or until golden brown. Remove from the oven and allow to cool before serving and enjoying.