Bring the milk to the boil in a wide saucepan. Stir in cocoa. Stir in rice pudding, bring to the boil again and let it swell at low heat for about 25 minutes.
In the meantime, drain the cherries and collect the juice. Fill up the juice with water at 1⁄2 l Stir starch, 1 tbsp sugar and 4-5 tbsp juice until smooth. Bring the rest of the juice to the boil, stir in the mixed starch, bring to the boil and simmer for at least 1 minute while stirring. Fold in cherries.
Finely chop the chocolate. Stir 3 tablespoons of sugar and vanilla sugar into the chocolate rice. Fold in the chocolate. Remove from the heat and let it rest for 10-15 minutes.
Whip the cream until semi-solid and fold into the chocolate rice. Serve the rice with some cherries. Add the rest.