Place butter, sugar and syrup in a saucepan over low heat. Cook, stirring, for 4 minutes or until smooth. Transfer to a large heatproof bowl. Stand for 10 minutes. Stir in egg. Sift over flours, cocoa powder, bicarbonate of soda and spices. Stir to combine. Turn dough out onto a lightly floured surface. Knead until dough no longer feels sticky. Wrap in plastic wrap. Refrigerate for 30 minutes.