Bring milk and sugar to the boil briefly. Leave the rice to swell on low heat for about 45 minutes. Stir at intervals. In the meantime clean, wash, halve and seed the grapes.
Boil up the grape juice. Stir cornflour and a little water until smooth and bind the juice, bring to the boil again. Add the prepared grapes. Season to taste with lemon juice and cinnamon. Season rice with vanilla sugar.
Cut off dumplings as desired and arrange in the grape sauce. Serve sprinkled with lemon balm and halved pistachios.