Heat the fat in a saucepan. Sprinkle with flour and sauté until light yellow. Stir in about 1 l water, wine and stock. Bring everything to the boil and simmer for about 5 minutes while stirring
Wash the dill, pluck the flags and cut finely, except for a little garnish. Whip cream until semi-stiff. Stir about 2/3 cream and dill into the soup. Season to taste with salt and pepper. Serve with remaining cream and prawns. Garnish with remaining dill