Put chopped chocolate, egg yolk and water in top of double saucepan. Stir over simmering water until chocolate has melted and mixture thickens slightly. Remove from heat, add Creme de Cacao and brandy; allow to cool. Mix cornflour to a smooth paste with the milk, add to chocolate mixture, stir until smooth. Stir over medium heat until sauce boils and thickens, reduce heat, simmer 2 minutes. Add cream, reheat without boiling.