Bring the buttermilk with the lemon zest to the boil. Shortly before, whisk through well with the whisk. Stir in the mixed pudding powder. For the semolina dumplings, bring the milk, butter and a little salt to the boil. Pour in the semolina and bake. Gradually stir in the eggs and possibly a little more flour. Cut off the dumplings with a tablespoon and place in the soup and cook. Beat the egg and sugar with the whisk to make sugar and season the soup with it.