Preheat oven to 400 degrees. Place chicken in roasting pan and set aside. Mix mustard, lemon juice, wine, garlic, pepper, rosemary and oil in a bowl and pour over chicken halves. Marinate for at least 4 hours or overnight. After fully marinated, add carrot, celery, onion and rosemary to roasting pan evenly around and under chicken. Season with salt and pepper. Roast in oven for 45 minutes or until juices run clear when pierced with a fork. Remove from oven and let settle. Cut into 8 pieces. Serve with Scarpariello Sauce.
Heat a medium size saute pan, add olive oil and saute for 1 minute. Add broccoli, mushroom and potatoes, saute for 2 minutes. Add chicken, wine and cook until wine reduces. Add chicken stock, cover and cook on low-flame for 10 minutes. To plate, remove chicken from pan and place on large platter. Add lemon, rosemary and butter to remaining sauce. Season to taste. Pour over chicken.