1. Thickly peel the kohlrabi to remove all the woody outer layer. Slice thinly and cook with the carrots, butter, 300 ml (1/2 pint) water and stock cube for about 10 minutes, until tender.
2. Blend the cornflour with very little cold water and strain in the vegetable liquid, stirring.
3. Return to the boil, stir in the dill and the fresh cream, then adjust seasoning. Bring almost to the boil and pour over the vegetables.