01 - Place the chicken breasts between two sheets of plastic wrap and pound them to an even thickness of about 1/2 inch using a meat mallet or rolling pin.
02 - In a mixing bowl, combine the buttermilk, 1 teaspoon of salt, and 1/2 teaspoon of black pepper. Add the chicken breasts, turning to coat evenly. Cover and refrigerate for at least 30 minutes, or up to 4 hours for maximum tenderness.
03 - In a separate bowl, whisk together the all-purpose flour, cornstarch, paprika, garlic powder, cayenne pepper (if using), 1 teaspoon of salt, and 1/2 teaspoon of ground black pepper until well combined.
04 - Remove each chicken breast from the buttermilk marinade, allowing the excess to drain off. Dredge each piece thoroughly in the seasoned flour mixture, pressing firmly to ensure the coating adheres well on all sides.
05 - Pour vegetable oil into a large skillet or deep pan to a depth of about 1/2 inch. Heat the oil over medium-high heat until it reaches 350°F (175°C), using a kitchen thermometer to verify the temperature.
06 - Carefully place the coated chicken breasts into the hot oil, working in batches to avoid overcrowding the pan. Fry for 6 to 7 minutes per side until the exterior is deep golden brown and the internal temperature registers 165°F (74°C).
07 - Transfer the fried chicken breasts to a paper-towel-lined plate to drain excess oil. Allow them to rest for 2 to 3 minutes before serving to let the juices redistribute.