Remove the duck giblets and set aside. Cut off each leg and thigh in one piece. Remove breasts whole from the bone. Chop the duck carcass and put it into a roasting pan with the onion and carrot. Roast for 45 minutes at 200ºC or until the bones are brown. Put browned bones and vegetables in a pot and add the demi-glace. Bring to a boil and simmer gently for an hour or more. Put the reserved liver and gizzard into a food processor with the veal and pork. Puree a few seconds and add egg (2 eggs if they are medium sized or smaller). Season with salt and pepper and continue to process. Add cognac and port and blend to a smooth texture. Carefully cut open the thigh of the duck and cut out the thigh bone. Fill the pocket created with the stuffing and fold the skin around it. Wrap the leg in buttered foil and bake in a 190ºC oven for an hour or until the internal temperature is 70ºC . Caramelize the sugar and water carefully and add vinegar. Cook until syrupy and strain in the duck-enriched brown sauce. Stir and simmer for 5 minutes and add blueberries. Heat oil and brown reserved breasts, skin side first. Remove from pan, cut off skin, and brown the breast again. Slice the browned breasts into strips and serve with the stuffed legs and sauce.