Remove the crusts from the bread and cut into cubes. Heat half the fat in a pan and roast the bread cubes in it while turning. Clean and wash the leek and cut into fine rings. Heat the rest of the fat in a saucepan and sauté the leeks for about 5 minutes.
Put something to garnish aside. Dust the remaining leek with flour and let it sweat. Add stock and cream while stirring constantly and bring to the boil. Puree the soup with a hand blender.
Season to taste with wine, salt and pepper. Serve garnished with leek rings, caraway and croutons.