Wash the duck breast and pat dry. In 1 tablespoon of hot clarified butter, fry on each side until golden brown. Season with salt, pepper and rosemary. Fry over medium heat for about 20 minutes.
In the meantime, remove 4 large outer savoy cabbage leaves and blanch in boiling water. Cut the remaining cabbage into slices, removing the stalk. Cut the cabbage into fine strips. Peel and finely chop the onion.
Heat the remaining clarified butter. Brown the onion and cabbage strips in it. Season with salt and pepper. Deglaze with cider and braise for about 10 minutes. In the meantime wash, cut into eighths and core the apples.
Swivel briefly in the frying fat of the duck breast. Remove breasts. Deglaze roast with stock, boil down for 3 minutes at high heat. Stir cornflour and a little water until smooth and thicken the sauce.
Season to taste with salt and pepper. Fill plenty of savoy cabbage strips into the large leaves, forming them into round shapes. Fry briefly in cabbage fat again. Cut open the duck breast and arrange with the cabbage balls on strips in the sauce.
Serve garnished with fresh herbs. Croquettes taste good with it.