There are almost as many variations of shortbread in Scotland as there are bakers. In Ayrshire the shortbread is a rich variety made with cream. Pitcaithly bannock is a festive shortbread made in a large round decorated with almonds and crystallised fruit.
Oatmeal shortbread is popular in Cupar, while Petticoat tails (round shortbreads shaped to look like petticoat hoops worn in the nineteenth century) came originally from Edinburgh. These and many others are all variations on a theme, but all good shortbread must be made with the best butter and high quality flour.
Cream the butter and sugar together well. Sift in the flours and salt and work in lightly with the fingertips until the mixture resembles fine breadcrumbs.
Press it together into two balls and turn out onto a board sprinkled with rice flour. Roll into round flat cakes about 1.3 cm ( 1/2 inch) thick. Pinch the edges all the way round with finger and thumb or press a fork all the way round, mark into slices with a knife and prick lightly all over with a fork.
Place on a baking sheet lined with greaseproof paper and bake at 150 °C / 300 °F / Gas 2 for about an hour. Leave to cool on the tin before transferring to a wire rack. Dust with caster sugar and divide into slices while still warm.