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 and submerge them completely. Marinate for at least 30 minutes, or up to 4 hours in the refrigerator for more 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 evenly combined.
04 - Remove the chicken from the buttermilk marinade, allowing excess liquid to drain off. Dredge each breast in the 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 to 350°F (175°C), using a kitchen thermometer to monitor the temperature.
06 - Carefully place the coated chicken breasts into the hot oil in batches, being careful not to overcrowd the pan. Fry for 6 to 7 minutes per side until golden brown and the internal temperature reaches 165°F (74°C).
07 - Transfer the fried chicken breasts to a paper-towel-lined plate to drain excess oil. Let rest for 2 to 3 minutes before serving.