1. Preheat oven to 400F.
2. Make a bouquet garni of thyme and rosemary. Stuff the chicken with the lemon and bouquet garni. Tie the chicken with butcher twine to bring the wings into the breast and the legs taught so the stuffing does not come out.
3. To prepare herb butter, combine butter, herbs, salt and pepper in a food processor; pulse until combined.
4. Place onion, celery, carrot and potatoes on the bottom of a roasting pan. Rub the chicken down with the herb butter and place on the roasting rack over the vegetables.
5. Roast chicken 10–15 minutes until the skin starts to brown. Lower the oven to 375F and continue cooking for another 45 minutes to an hour, or until a thermometer placed into the thickest part of the thigh reads 155F. Allow the chicken to rest.
6. While resting pour the pan drippings into a skillet and add the butter, Dijon and parsley. Stir on low heat until the sauce thickens. Place vegetables on a platter. Top with cut-up chicken and serve with pan sauce.