Preheat oven to 160C (140C fan-forced). Lightly grease a deep 23cm round cake pan and line with baking paper, making sure the paper extends 10cm above the top of the pan.
Sift the flours, cocoa and bicarb together in a large mixing bowl, stirring until well combined.
Place coffee into a jug and top up with boiling water to 180mls.
Pour coffee into a large saucepan over very low heat, add butter, sugar and chocolate, stirring to combine. Continue stirring until chocolate and butter have melted and the mixture is smooth. Set aside to cool slightly. Add eggs, oil and milk to the chocolate mixture, whisking until well combined.
Create a well in the centre of the flour mixture and pour the chocolate mixture into the centre, stirring until well combined. Pour the mixture into the prepared cake pan. Place pan on an oven tray and bake in oven for 2 hours or until a skewer comes out of the centre cleanly. Remove from oven, place on a wire rack and allow cake to cool completely in the pan.
Place cream in small saucepan and heat over low heat until just below boiling point. Remove from heat, add chocolate and stir gently. Leave to stand for several minutes, then stir gently again. Do not stir too much. Repeat process until chocolate has melted and mixture is smooth and shiny.
Allow to cool until thick enough to spread, then apply to top and sides of cake with a spatula.