Place chicken pieces in a large bowl. Pour buttermilk and hot sauce over the chicken. Mix to coat completely. Cover and refrigerate for at least 4 hours, or preferably overnight.
In a shallow dish, whisk together the flour, cornstarch, salt, pepper, paprika, garlic powder, and cayenne pepper. This is your dredge mixture.
Remove chicken from the buttermilk, letting excess drip off, but do not wipe dry.
Dredge each piece thoroughly in the flour mixture, pressing the flour onto the chicken to create a thick, craggy coating. For extra crispiness, dip the floured chicken back into the remaining buttermilk for a second, quick dip, and then dredge again in the flour mixture.
Heat 2 inches of vegetable oil in a deep, heavy-bottomed pot or Dutch oven to 325 degrees F. Use a thermometer to maintain the temperature.
Carefully place chicken pieces into the hot oil, ensuring you do not overcrowd the pot. Work in batches.
Fry chicken for about 6 to 8 minutes per side, turning occasionally, until deep golden brown and cooked through (internal temperature should reach 165 degrees F). Adjust heat as needed to prevent burning the crust before the inside cooks.
Remove chicken from the oil and place it on a wire rack set over a baking sheet to drain excess oil. Do not place on paper towels, as this can steam the crust and make it soft.
Serve hot.
Notes
For the crispiest crust, ensure your oil temperature stays steady between 300 and 335 degrees F during frying.
If you are cooking larger pieces like breasts, you may need to finish them in a 350 degree F oven after frying for 5 minutes to guarantee they are cooked through without burning the exterior.