Place chicken in baking pan. Sprinkle with salt and pepper. Mix the mustard, syrup, and vinegar together and pour over chicken. Place in oven and bake 45 minutes. Baste with sauce and turn chicken a couple of times during cooking.
When the chicken is down to its last 10 minutes. Place baby broccoli in boiling water for 3 minutes. Drain and place in ice bath. Place butter in saute pan. Add the baby broccoli and saute until tender adding salt and pepper.
Remove chicken from oven. Sprinkle with rosemary. Spoon some sauce over chicken and serve with baby broccoli