Mix the cocoa with one cup of cold tap water, stir and set aside. In another bowl sift the flour with the bicarb – and set this aside. Beat together the butter and sugar until light and fluffy. Add the eggs one at a time and beat well in between. Add bit by bit the cocoa mixture and the flour mixture alternatively until all mixed well. Pour in a greased round cake tin and bake for 1 hour at 180 degrees. Allow the cake to cool in the tin. Serve with chocolate icing.