01 - Place chicken breasts between two sheets of plastic wrap and pound to an even 1/2-inch thickness using a meat mallet or rolling pin.
02 - In a mixing bowl, whisk together buttermilk, 1 teaspoon salt, and 1/2 teaspoon black pepper until combined.
03 - Submerge chicken breasts in the buttermilk mixture. Cover and refrigerate for at least 30 minutes, or up to 4 hours for maximum tenderness.
04 - In a separate shallow bowl or dish, combine flour, cornstarch, paprika, garlic powder, cayenne pepper (if using), remaining salt, and black pepper. Whisk until evenly distributed.
05 - Remove chicken from the marinade, allowing excess buttermilk to drain. Press each breast firmly into the flour mixture, coating both sides thoroughly and shaking off any excess.
06 - Pour vegetable oil into a large skillet or deep pan to a depth of about 1/2 inch. Heat over medium-high to 350°F, using a kitchen thermometer to monitor temperature.
07 - Carefully place chicken breasts in the hot oil, working in batches to avoid overcrowding. Fry for 6 to 7 minutes per side until golden brown and the internal temperature reaches 165°F.
08 - Transfer fried chicken to a paper-towel-lined plate to drain. Let rest for 2 to 3 minutes before serving.