Start by dipping the rabbit pieces into flour, coating them completely. (This will help to thicken the wine sauce). In a large pan, heat the oil and butter till hot, and then add the garlic and rabbit pieces. Brown the rabbit pieces on both sides, as this will seal in their juices. It should take around 5 or 6 minutes. Remove the rabbit pieces from the pan, and put to one side while you continue to cook the remaining ingredients. In the same pan, add the whole shallots, celery and carrots and soften for 5 minutes. Tie up the thyme, rosemary and bay leaves with some string, and then pop them into the pan, along with the browned rabbit pieces. Pour over the red wine and chicken stock, season well with pepper and salt, and bring to the boil. Add the dried chestnuts, lower the heat, and leave to simmer for about 45minutes, to an hour. By this time the rabbit and vegetables should be soft and tender. Remove the herbs from the pan, and add the piece of chocolate to the pan. Mix the chocolate so that it melts into the red wine sauce. The sauce should be thick enough to serve, but if it is too loose, thicken slightly with some corn flour. When ready, serve the rabbit in large deep plates, with the delicious red wine sauce with tender vegetables. Sprinkle with parsley and serve with garlic and herb mash, and warm crusty bread.