Duck wash. Peel and halve the onions. Place the duck in a large pot with water so that the duck is completely covered. Add salt, onions and marjoram, bring to the boil, cover and cook over medium heat for about 1 hour.
In the meantime, clean the savoy cabbage, quarter it and remove the stalk. Wash the cabbage and cut into slices. Put cabbage in boiling salted water, bring to the boil and cook for about 8 minutes. Pour into a sieve and drain well.
Lift the duck out of the water, drain very well and let it cool down a little. Then rub the duck inside and out with salt and pepper. Place on a fat pan of the oven and roast in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 1 1/2 - 1 3/4 hours.
Bring the stock to the boil. After about 1 hour of frying time, remove the fat pan from the oven. Spread cabbage and bacon around the duck, add boiling broth and put it back into the oven. Pour the stock from the fat pan over the duck several times.
Remove from oven, keep cabbage warm. Cut the duck into portions and arrange on a plate with the cabbage. Garnish with marjoram.