Heat the fat in a saucepan. Sweat flour in it, deglaze with broth and wine. Bring to the boil and simmer for about 5 minutes. Season to taste with salt and pepper. Whip cream until half stiff and stir 2/3 into the hot soup.
Add the crab meat. Wash the dill, pluck flags from the stalks and chop finely. Serve the soup garnished with the remaining cream and dill.