Draw around an 8-inch template on greaseproof paper and flip the paper over.
Sieve the plain flour into a bowl.
Add the caster sugar to the flour.
Dice cold unsalted butter into small cubes.
Rub the butter into the flour and sugar mixture until it resembles rough breadcrumbs or wet sand.
Bring the mixture together in the bowl until a smooth, non-sticky ball is formed.
Flatten the ball into a disc and place it in the middle of the template on the greaseproof paper.
Dust the top of the dough and the rolling pin with flour.
Roll out the dough until it meets the edges of the drawn circle.
Smooth the edges to make it round and neaten any cracks.
Cut the dough into wedges (e.g., eight pieces) about halfway through, not all the way.
Crimp the edges by pinching the dough and pressing with a finger, or use the tines of a fork.
Randomly prick the dough with a fork.
Refrigerate the dough for about 15 minutes.
Sprinkle more caster sugar or granulated sugar over the dough.
Bake in the middle of the oven at a low temperature (150c Fan) for 30-35 minutes, until the edges are tinged golden brown.
Go over the cut lines again with a knife while the shortbread is still warm.
Transfer the shortbread to a wire rack to cool completely.
