Peel and wash the carrots and kohlrabi. Quarter the kohlrabi. Cut the vegetables into slices. Boil 1/2 litre water and broth. Add vegetables and cook for about 10 minutes. Heat oil in a pan and fry the meatballs for about 10 minutes, turning occasionally.
Mix sour cream, cornstarch and egg yolk. Add the sour cream mixture to the vegetables while stirring constantly and bring to the boil briefly. Remove from the heat immediately and season to taste with salt, pepper and sugar.
Add the meatballs and stir in the basil.