Roughly chop the chocolate and bring to the boil with 400 ml of the milk. Meanwhile, mix the remaining 100 ml milk with cornstarch, sugar and desiccated coconut. When the milk boils and the chocolate has melted, remove the pan from the stove. Add the coconut mixture and stir everything with a whisk. Simmer on low heat while stirring until a pudding-like consistency is formed. Fill into bowls and let cool or enjoy warm.