In a pan, whisk the milk with all the other ingredients up to and including the egg. Add the chocolate, bring to the boil over a medium heat, stirring constantly. As soon as the mixture thickens and turns creamy, remove the pan from the heat and continue whisking for approx. 2 mins. Pour the custard into a bowl through a sieve, allow to cool, then cover and refrigerate for approx. 2 hrs. Stir the custard until smooth just before serving.