1.Preheat the oven to 160°C (140°C fan-forced). Line two large oven trays with baking paper.
2.Beat butter, icing sugar and extract in a small bowl with an electric mixer until light and fluffy; transfer mixture to a large bowl. Stir in the sifted flours and cocoa in two batches. Turn the dough onto a lightly floured bench and knead lightly for 5 minutes.
3.Divide mixture into six equal portions. Use your hands to press each dough portion into a 12cm round. Mark each shortbread round into 6 wedges with the back of a large knife, then prick with a fork. Use your finger tips to pinch the edges of rounds; sprinkle with the coffee crystals.
4.Bake for about 45 minutes or until cooked through. Cool on trays.