Place the duck carcasse and legs into a 5 l pot, the add the onions, carrots, celery and parsnip. Add water just enough to fill more than 2/3 of the pot. Add salt, one teaspoon of black peppercorns and the parsley stems.
Cover with a lid and let it simmer on low heat for about 2 hours. Use a slotted spoon to skim all the impurities that are formed at the surface during cooking.