Add the flour, cornstarch, paprika, creole seasoning, garlic powder, onion powder, dried thyme, bouillon powder, cayenne pepper, black pepper, and salt on a large plate. Mix till fully combined.
Working with one piece at a time, remove the marinated chicken from the buttermilk soak, letting the excess drip back into the bowl. Then dredge it in the flour mixture, pressing it so the seasoned flour adheres to all sides, then shake off the excess flour. You could use a Ziploc bag for this process, too.
Transfer the coated chicken to a tray and let it rest for 10-15 minutes while preparing the oil. This will help the coating to stay on better.
Heat oil in a deep fryer or cast iron skillet to 375℉/190℃. The temperature will drop once you add chicken.
Using tongs, slowly and carefully place the chicken in the hot oil. Work in batches, and don't overcrowd the skillet.
Fry the chicken until golden brown, turning once every 10-15 minutes – depending on the size of the pieces. Chicken is done when it is no longer pink inside and the juices run clear, or your instant-read thermometer reads 165℉/75℃. You may do a test by piercing the chicken with a fork.
Drain the chicken on paper towels and then transfer them to a wire rack.
Repeat with remaining chicken pieces. Let them cool for at least 10 minutes before serving.