Clean the carrots and kohlrabi and cut into 1 cm cubes and add enough vegetable stock (cold) to cover the vegetables. Bring to the boil and cook covered for about 10 minutes.
Then add the cream, bring to the boil again and boil down in the open saucepan until the liquid is creamy. Add the herbs and butter towards the end (depending on your taste). If necessary tie with a light sauce thickener.