Truss the chicken and place it in a large freezer bag
Combine all remaining ingredients in a bowl and mix well
Pour the buttermilk mixture into the freezer bag with the chicken and coat the chicken well
Let rest in the refrigerator for at least 4 hours, 24 hours is best
Preheat oven to 375F
Remove the chicken from the bag and drain off excess buttermilk, strain the marinade and brush chicken with extra rosemary and buttermilk marinade
Place chicken in a roasting pan, roast for 20 minutes, rotate pan and roast another 20 minutes
Continue to rotate every 10 minutes, until an instant-read thermometer reads 165F in the thickest part of the thigh, but not touching a bone.
Remove from the oven once it reaches 165F, brush lightly with olive oil, cover with foil and let rest for 10-15 minutes.
