1. COMBINE water, sugar, butter, Cocoa and bicarbonate soda in a saucepan and warm, but do not boil, stirring until the sugar has dissolved. Then bring to the boil and simmer gently for 2 minutes. Transfer mixture to a bowl and cool for 30 minutes.
2. ADD the flour and eggs and beat until just combined. Pour into a greased and base-lined 20cm cake pan. Bake in a moderate oven 180°C for 40 minutes or until cooked. Cool for 10 minutes before turning onto a wire rack to cool completely.
3. SIFT together the icing mixture and Cocoa. Mix in the butter and enough hot water to form a soft icing. Spread over the cooled cake and decorate as desired.