Heat 1/3 litre of milk in a saucepan with the broken chocolate and cocoa. Stir with a whisk and bring to the boil. This will bring out the aromas. Keep at a low boil for 3 minutes while stirring with the whisk to prevent it from sticking and burning.
Dilute the starch in a little of the remaining cold milk. Pour with the rest of the cold milk into the saucepan, still stirring with the whisk. Cook until it boils and thickens, stirring constantly.
Serve hot to taste, or as a dessert covered with whipped cream and slivered almonds, why not! :)