- Preheat oven to 180°C/160°C fan-forced. Grease a 6cm-deep, 22cm round cake pan. Line base and sides with baking paper.
- Melt butter in a large saucepan over medium-low heat. Add chocolate, sugar and 1 cup cold water. Cook, stirring constantly, for 3 to 4 minutes or until smooth. Transfer to large bowl. Cool for 10 minutes.
- Add eggs. Stir to combine. Add flours and cocoa. Stir until smooth. Pour mixture into prepared pan. Bake for 1 hour and 30 minutes or until a skewer inserted in the centre has moist crumbs clinging. Stand for 10 minutes in pan. Turn out onto a wire rack to cool.
- Meanwhile, make chocolate ganache: Place chocolate and cream in a small saucepan over medium-low heat. Cook, stirring constantly, for 3 to 4 minutes or until smooth. Transfer to a bowl. Refrigerate for 30 minutes or until thick enough to spread.