01 - Place the chicken breasts between two sheets of plastic wrap and pound to an even 1/2-inch thickness using a meat mallet.
02 - Whisk together the buttermilk, 1 teaspoon salt, and 1/2 teaspoon black pepper in a bowl. Submerge the chicken breasts and marinate for at least 30 minutes, or refrigerate up to 4 hours for greater tenderness.
03 - In a separate bowl, combine the flour, cornstarch, paprika, garlic powder, cayenne pepper (if using), remaining salt, and black pepper. Mix thoroughly.
04 - Remove the chicken from the marinade, allowing excess to drip off. Dredge each breast in the seasoned flour mixture, pressing firmly so the coating adheres evenly.
05 - Pour vegetable oil into a large skillet or deep pan to a depth of about 1/2 inch. Heat to 350°F over medium-high heat.
06 - Carefully lower the chicken into the hot oil in batches without overcrowding. Fry 6 to 7 minutes per side until deep golden brown and the internal temperature reaches 165°F.
07 - Transfer the fried chicken to a paper-towel-lined plate and let rest 2 to 3 minutes before serving.