Place the chicken pieces in a large bowl. Pour buttermilk over the chicken, ensuring all pieces are submerged. Stir in the hot sauce. Cover and refrigerate for at least 4 hours, or preferably overnight.
In a shallow dish, whisk together the flour, cornstarch, baking powder, salt, pepper, paprika, garlic powder, and cayenne pepper. This is your dredge mixture.
Remove the chicken from the buttermilk, letting excess drip off, but do not rinse.
Dredge each piece thoroughly in the flour mixture, pressing the coating onto the chicken to create a thick, craggy surface. For extra crispiness, dip the floured piece back into the remaining buttermilk for a second, quick dip, then return it to the flour mixture for a final coat.
Heat 2 to 3 inches of oil in a deep, heavy-bottomed pot or Dutch oven to 325 degrees F. Use a thermometer to monitor the temperature.
Carefully place 3 to 4 pieces of chicken into the hot oil, ensuring you do not overcrowd the pot, which lowers the oil temperature.
Fry the chicken for about 6 to 8 minutes per side, turning occasionally, until deep golden brown and cooked through (internal temperature reaches 165 degrees F). Thicker pieces like breasts may take longer.
Remove the chicken from the oil and place it on a wire rack set over a baking sheet to drain excess oil. Do not place directly on paper towels, as this steams the bottom crust.
Let the chicken rest for 5 minutes before serving.
Notes
For the crispiest results, maintain the oil temperature between 300 and 325 degrees F during frying.
If you are cooking larger pieces like breasts, you can finish them in a 350 degree F oven after frying for 5 minutes to guarantee they are cooked through without burning the crust.
Use chicken pieces that are similar in size for even cooking.