Season chicken pieces on all sides with 1 tsp seasoned salt and ½ tsp black pepper. Place into an oblong baking dish and cover with 2 ½ cups buttermilk. Turn to coat. Chill overnight, turning once.
30 minutes before frying: Remove chicken from buttermilk, discard marinade. On a plate sift together the flour, cornstarch, 2 tsp seasoned salt, 1 tsp black pepper, garlic powder, onion powder and paprika.
In a large shallow bowl whisk together the eggs, ½ tsp salt, ½ tsp black pepper, ½ cup buttermilk and hot sauce.
Dredge chicken pieces in flour, into egg wash then into flour again. Arrange on a baking sheet. Let stand for 30 minutes to bring to room temperature and set breading.
To fry: Preheat the oven to 200°F. Prepare a rimmed baking sheet with an oven safe baking rack. Set aside.
Fill a 12-inch cast iron skillet about ⅓ full with oil. Heat to 350°F. Carefully lower chicken pieces in oil. Fry dark meat and white meat separately.
Maintain oil temperature around 350°F. Fry chicken in batches cooking dark meat pieces and white meat separately. Cook for 10-15 minutes per side or until juices run clear and the internal temperature reaches 165°F. Turn carefully using tongs to avoid splatters.
Place fried pieces on rack and keep warm in oven between batches.
Rest for 10 minutes before serving.