Cream together the butter and caster sugar in a large mixing bowl using a wooden spoon or electric mixer.
Add the flour and mix until you have a soft dough (add any additional fillings such as dark chocolate chips. Wrap the dough in cling film and place in the fridge for 15-30 minutes.
Preheat the oven to gas mark 4 or 180 degrees Celsius.
On a floured surface, roll out the biscuit dough to 1.5 cm thick and use circular cutters to cut out your shortbread biscuit shapes.
Place on a non-stick or lined tray and bake in the oven for 15-20 minutes or until all of the biscuits are starting to look golden.
Place the biscuits onto a wire rack to cool and enjoy.