Clean, wash and cut the rhubarb into pieces. Boil 3/8 litres of water. Add rhubarb and raspberry jelly and simmer for about 4 minutes. Remove lemon peel. Stir the starch with a little water until smooth and bind the rhubarb with it, bring to the boil again. Bring milk and lemon peel to the boil. Add sugar, vanilla sugar and semolina.
Turn off the heat and stir until the dough comes off the bottom of the pot. Stir in egg. Bring slightly salted water to the boil. Use 2 teaspoons of the semolina to cut off small dumplings, add to salted water and cook over a low heat for about 10 minutes. Serve the rhubarb groats with the semolina dumplings. Decorate with lemon balm