01 - Place chicken breasts between two sheets of plastic wrap and pound to an even 1/2-inch thickness using a meat mallet.
02 - Whisk together buttermilk, 1 teaspoon salt, and 1/2 teaspoon black pepper in a shallow bowl. Submerge chicken breasts in the mixture, cover, and refrigerate for at least 30 minutes or up to 4 hours for maximum tenderness.
03 - In a separate wide bowl, combine flour, cornstarch, paprika, garlic powder, cayenne pepper (if using), remaining 1 teaspoon salt, and 1/2 teaspoon black pepper until evenly blended.
04 - Remove chicken from the buttermilk, allowing excess to drip off. Press each breast firmly into the seasoned flour mixture, ensuring full coverage on all sides.
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, verifying temperature with a kitchen thermometer.
06 - Carefully lower chicken breasts into the hot oil in batches without overcrowding. Fry 6 to 7 minutes per side until deeply golden brown and internal temperature reaches 165°F.
07 - Transfer fried chicken to a paper-towel-lined plate and let rest 2 to 3 minutes before serving to allow juices to redistribute.