Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper and place an oven-safe wire rack on top. Lightly grease the rack with cooking spray.
Pat the chicken completely dry with paper towels. Pound each piece to an even ½-inch thickness. Season both sides with the kosher salt and black pepper.
In a shallow bowl, whisk together the flour, cornstarch, kosher salt, garlic powder, onion powder, paprika, and black pepper.
In a second shallow bowl, whisk together the eggs, buttermilk, and kosher salt until smooth.
In a third shallow bowl, combine the crushed cornflakes, kosher salt, garlic powder, onion powder, paprika, smoked paprika, black pepper, parsley, baking powder, and cayenne pepper, if using.
Dredge each piece of chicken in the flour mixture, shaking off any excess.
Dip the chicken into the egg wash, allowing any excess to drip off for a few seconds.
Press the chicken firmly into the cornflake mixture until evenly coated on all sides.
Arrange the coated chicken on the prepared wire rack. Let it rest for 10 minutes to help the coating adhere.
Lightly spray the tops with cooking spray or drizzle very lightly with melted butter.
Bake for 10–12 minutes.
Carefully flip the chicken, rotate the baking sheet, and lightly spray any dry spots if needed. Continue baking for another 10–14 minutes, or until the thickest part reaches 162–163°F (72–73°C).
If desired, broil for 30–60 seconds for extra golden color, watching carefully to prevent the cornflakes from burning.
Remove the chicken from the oven and let it rest on the wire rack for 5 minutes. The internal temperature will rise to 165°F (74°C).
Serve immediately with mashed potatoes, roasted vegetables, coleslaw, mac and cheese, or your favorite dipping sauces.