Heat oven to 400°F. Pour buttermilk into large shallow dish. In large plastic food-storage bag, mix flour, salt and pepper. Dip each chicken piece in buttermilk, then place in bag with flour. Hold bag closed and shake until chicken is coated. Place skin side down in ungreased 15x10x1-inch pan. Spray chicken generously with cooking spray. Turn chicken; spray other sides generously with cooking spray.