Start by placing the chicken breasts between two long sheets of plastic wrap. Using a meat mallet or rolling pin, pound the chicken to an even thickness of about 1/2 inch. This will ensure even cooking and tenderness. Slice the chicken into portions slightly larger than your buns; any leftover bits can be made into delicious nuggets.
In a large bowl, whisk together the buttermilk, egg, and salt. Set aside 2 tablespoons of this mixture for later. Add the chicken pieces to the bowl, ensuring they are well coated in the marinade. Cover the bowl and let the chicken marinate in the fridge for at least 1 hour, but ideally up to 24 hours. This allows the flavors to meld beautifully.
While the chicken is marinating, prepare the breading mixture. In a separate bowl, combine the flour, cornstarch, garlic powder, onion powder, paprika, mustard powder, the reserved buttermilk mixture, salt, black pepper, and cayenne pepper. Mix these ingredients well; the aim is to create small clumps to add extra crunch when frying.
Next, heat the vegetable oil in a large, heavy pot over medium-high heat. If you have a thermometer, clip it to the side of the pot and heat the oil to around 350°F. Maintaining a consistent temperature is crucial for achieving that golden, crispy exterior.
Once the oil is hot, use tongs to lift the marinated chicken from the bowl, letting the excess marinade drip off. Dredge the chicken in the breading mixture, pressing it onto both sides to ensure a good coating. Shake off any excess breading.
Carefully lower the coated chicken into the hot oil. Fry each piece for about 2 minutes without moving it to ensure it forms a crust. After 2 minutes, flip the chicken and fry for another 2 minutes until golden brown and crispy. Use a wire cooling rack to transfer the chicken so they can drain and remain crispy.
Repeat the frying process with any remaining chicken, frying no more than two pieces at a time to avoid overcrowding the pot. Keep an eye on the oil temperature, adjusting the heat as necessary to maintain that perfect frying temperature.
While the chicken is cooling, lightly butter the brioche buns on the cut sides. Toast them in a dry skillet over medium heat until golden brown. This step adds flavor and prevents the buns from becoming soggy.
Assemble your sandwiches by generously spreading the Chick-Fil-A sauce on both sides of the toasted buns. Start with a layer of lettuce, followed by a piece of fried chicken, some slices of tomato, and if desired, a slice of cheddar cheese. Add pickles for that extra crunch!
Finally, place the top bun on your masterpiece and serve immediately. Enjoy the crispy, juicy goodness of your freshly made Crispy Chicken Sandwich!
