Wash the cucumber and cut into pieces without peeling. Peel and chop the onion.
Put the cucumber pieces with onion, water, milk, flour, butter and spices in the Thermomix and cook for 10 minutes on level 1 at 100 ° C. Just before the end of the cooking time, add the mixed herbs and sour cream or crème fraiche.
Pour the soup onto plates and garnish with a dollop of sour cream and some fresh dill.