Place cornflakes into a plastic zip top bag, and use a rolling pin to break them into pieces. Set aside.
Whisk the buttermilk, mustard, 2 teaspoons salt, 1 teaspoon of the garlic powder, 1 teaspoon black pepper, and hot sauce together in a large bowl.
Add the chicken, turn to coat well, cover with plastic wrap, and refrigerate at least 1 hour.
Preheat oven to 400 degrees F with oven rack at upper middle position.
Line a rimmed baking sheet with foil, place a wire rack on top, and coat the rack with vegetable oil spray.
Prepare coating by pulsing the bread in a food processor to coarse crumbs, about 8 pulses. Then gently toss the cornflakes, breadcrumbs, remaining ½ teaspoon garlic powder, ½ teaspoon black pepper, ¼ teaspoon salt, poultry seasoning, paprika, and cayenne together.
Place in a shallow dish. Drizzle oil over the crumb mixture and toss until well coated.
Coat chicken: Working with one piece at a time, remove the chicken from the marinade and dredge in the crumb mixture, firmly pressing the crumbs into all sides of the chicken. Use your hands to press the crumb mixture into place.
Place the chicken on the prepared wire rack, leaving ½ inch of space between each piece so there is room for air to flow between and help it get crispy!
Bake 35-45 minutes, until the chicken is deep golden brown and the thickest part registers 160 degrees on an instant read thermometer.
Remove from oven and let chicken rest 5 minutes before serving.