I think shortbread has to be at least 1.5cm thick, better still 2cm, to yield a truly satisfying bite. I like the decorative rounds marked into portions and I own at least two antique shortbread moulds that are used to press fancy designs on the finished round, but my favourite is chunky shortbread fingers pricked with the tines of a fork.
600g plain flour
125g ground rice
250g caster sugar
500g butter, cut into 2cm dice and chilled for an hour
Mix the dry ingredients together in an electric mixer or give a quick pulse in a food processor. Add the butter and mix on low speed in an electric mixer, or use the pulse button in a food processor until the dough just comes together.
Tip on to the workbench, knead lightly and press into a round. Wrap and chill for 30 minutes. Roll out to 1.5cm or 2cm thickness and cut to desired shape.
Chill again for at least an hour, preferably overnight.
Preheat oven to 160C.
Arrange shapes well apart on a paper-lined baking tray and bake until golden, about 12 minutes.