Preheat the oven to 250 degrees. Brown the saddle of venison all around in butter and oil. Place the meat in the hot oven and reduce the temperature to 175 degrees. Roast for another 7 minutes. Cover and let rest. Stir the game stock through the roasting juices and sieve the gravy. Stir in olive oil and cubes of cold butter, and cook the gravy briefly. Add the citrus peels, salt and pepper to taste and a drop of vinegar to the gravy. Cut the venison between the bones into chops. Spoon the sauce over the chops and serve. On a plate or on a platter.