Combine the buttermilk in a large bowl with the hot sauce, 1 tablespoon salt and 1 teaspoon black pepper. Add the chicken pieces and turn to coat. It's best if they're submerged.
Marinate for at least 4 hours and up to 12 hours.
Combine the flours in a shallow dish, a pie plate works well. Season the flour mix with a heaping tablespoon of salt and at least a teaspoon of pepper.
Meanwhile, pour the oil into a heavy skillet, preferably cast iron, to about 2 1/2 to 3 inches deep. Heat the oil over medium high heat until it is 350 degrees when tested with a thermometer.
Pull each piece of chicken out of the buttermilk marinade, letting the excess drip back into the bowl. Dredge the chicken in the flour mixture and make sure its well-coated. Allow excess to shake off.
Rest the chicken on a sheet pan fitted with a rack (I use my cooling rack) until it's all been coated with the flour mixture and the oil is to temperature.
When the oil is ready, turn the oven on to 350 degrees.
Using tongs, put the chicken pieces in the hot oil until golden brown, about 3 minutes per side. Don't crowd the pan when you do this. Also, check the temperature of the oil throughout and adjust the heat under the pan to try and maintain 350 degrees.
As you take the chicken pieces out of the oil, set them back on the racks on the sheet pan. When all the chicken is fried, put the pan into the oven and let it finish cooking. This should take only 15 to 20 minutes.