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 buttermilk, 1 teaspoon salt, and 1/2 teaspoon black pepper. Add the chicken breasts, turning to coat evenly. Cover and refrigerate for at least 30 minutes, or up to 4 hours for enhanced tenderness.
03 - In a separate bowl, whisk together all-purpose flour, cornstarch, paprika, garlic powder, cayenne pepper (if using), 1 teaspoon salt, and 1/2 teaspoon ground black pepper until well combined.
04 - Remove each chicken breast from the buttermilk brine, allowing excess liquid to drain off. Dredge each piece thoroughly in the seasoned flour mixture, pressing firmly to ensure the coating adheres on all sides.
05 - Pour vegetable oil into a large skillet or deep pan to a depth of about 1/2 inch. Heat over medium-high heat to 350°F (175°C), using a kitchen thermometer to verify temperature.
06 - Carefully place chicken breasts into the hot oil in batches, avoiding overcrowding. Fry for 6 to 7 minutes per side until deep 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. Allow to rest for 2 to 3 minutes before serving for optimal juiciness.