- Grease a 17 x 27cm slice tin with butter. In a bowl, beat the butter and caster sugar until pale and creamy.
- Sift flour, cocoa, cinnamon and salt over the creamed mixture, then stir to combine. Spread the mixture evenly over the base of the prepared tin and prick all over with a fork.
- Score the surface where you will cut the shortbread in fingers or bars. Chill for 20 minutes while the oven heats to 180 degC.
- Bake for 25 minutes or until firm to the touch. Remove from the oven and, while still hot, sprinkle surface with sugar, then leave to cool completely in the pan. Slice into fingers or bars to serve.