Onions peel and very finely dice. Peel garlic and chop finely. Heat the fat in a pot. Sauté garlic and onions in it, dust with flour and sauté briefly. Add wine, then cream and 400 ml broth, season with salt and pepper.
Let simmer for about 10 minutes.
Wash the meat, dab dry, cut the skin crosswise and season all around with salt. Place the skin side in a cold, coated pan. Fry over medium heat for about 5 minutes. Turn the breast and fry for another 3 minutes.
Put the duck breast on the fat pan of the oven. Roast in the preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see manufacturer) for approx. 12 minutes.
Clean, wash and cut the leek into rings. Heat the oil in a pan and sauté the leek in it. Deglaze with 100 ml stock and cook for about 4 minutes. Grate cheese finely, stir into the soup and dissolve in it.
Cut the meat into thin slices. Spread leek and meat on bowls. Add soup and sprinkle with fried onions.