1.Preheat oven to 160°C (140°C fan-forced). Grease a 23cm-square slab pan. Line base and sides with baking paper.
2.Combine butter, chocolate, sugar, water, whisky and coffee in a medium saucepan. Stir over low heat, until mixture is smooth; cool. Stir in sifted flours and cocoa, then eggs.
3.Pour mixture into pan. Bake 1 hour 15 minutes. Stand for 10 minutes. Turn onto wire rack to cool. Serve dusted with cocoa powder or icing sugar, if desired.