Marinate the chicken in buttermilk. Place the chicken pieces in a large bowl, pour the buttermilk over them, and ensure they are fully submerged. Cover and refrigerate for at least 2 hours, preferably overnight for best flavor and tenderness.
In a shallow dish or plate, whisk together the flour, paprika, garlic powder, onion powder, oregano, thyme, salt, black pepper, and cayenne pepper if using.
Heat the vegetable oil in a deep frying pan or Dutch oven over medium-high heat. Ensure that there is enough oil to submerge the chicken pieces halfway (about 2 inches deep). The oil should reach a temperature of around 350°F (175°C).
Remove the chicken from the buttermilk and allow the excess to drip off. Dredge each piece of chicken in the seasoned flour mixture, making sure to coat it thoroughly. Shake off any excess flour.
Carefully place the coated chicken in the hot oil, being careful not to overcrowd the pan. Fry in batches if necessary. Cook the chicken for about 10-12 minutes on one side, then flip and cook for an additional 8-10 minutes, or until the outside is golden brown and the internal temperature reaches 165°F (75°C).
Once cooked, transfer the chicken to a plate lined with paper towels to drain any excess oil.
Serve your homemade KFC chicken hot, with your favorite sides.