Put half a liter of milk in a saucepan. Slit the vanilla pods lengthways and scrape out the pulp. Add the vanilla pulp, pods and salt to the milk and bring to the boil, then remove the pods. Roughly chop the block chocolate, add and melt while stirring. Mix the sugar with cocoa, cornstarch and the remaining milk in a bowl until smooth, pour into the hot chocolate milk and bring to the boil again. Rinse four serving dishes with cold water, fill in the burner, let cool and put in the refrigerator for at least 2 hours. Before serving, remove the flammeri from the edge of the pan with a sharp knife and turn it onto 4 plates. Sprinkle with chocolate flakes if you like.