Preheat oven to 140C. Grease and line a deep, 23cm square baking tin.
For the shortbread base, beat the sugar and butter until pale and well combined – a hand-held electric mixer works best, but if your butter is soft, you can do this with a wooden spoon.
Once the sugar and butter mix is pale in colour, add the flour. Beat it again but only for a moment, until the mixture resembles sandy breadcrumbs.
Tip the mixture into the lined tin, pressing down very lightly so it becomes level.
Bake for 30-40 minutes or until pale golden in colour and cooked through. Sprinkle with caster sugar immediately, then allow to cool for 15 minutes.
Slice into your chosen shape, then cool before removing from the tin.
Aran: Recipes And Stories From A Bakery In The Heart Of Scotland by Flora Shedden, £22, is out now.
Enjoy the convenience of having The Sunday Post delivered as a digital ePaper straight to your smartphone, tablet or computer.
Subscribe for only £5.49 a month and enjoy all the benefits of the printed paper as a digital replica.