Roast duck carcass in 300°F oven for 30 minutes. Remove carcass and place in large pot with cold water until body is fully submerged. Let boil for 2 hours. Remove all solid items and discard. I like to use a chinoise which is a conical strainer used for making perfectly smooth soups and sauces. Once you have your clean duck stock, pour into a sauce pan, add caramel and juice of 2 oranges. Reduce till you get a thick consistency. If you would like a thicker consistency, add 1 teaspoon of cornstarch diluted with ½ teaspoon of water and then bring back up to boil.