Place the chicken pieces on a wire rack set over a half-sheet pan and sprinkle on all sides with the salt. Set aside at room temperature for 30 minutes.
Combine the black pepper, sumac, cayenne, and garlic powder in a small bowl, then divide the blend into two equal portions (total mixture = 6 teaspoons). Sprinkle the chicken on all sides with half of the spice mixture, then refrigerate, uncovered, for at least 4 hours (overnight would be better).
Remove the chicken from the refrigerator 30 minutes before cooking. Whisk together the flour, cornstarch, and the remaining spice mixture in a large bowl. In another bowl, whisk together the buttermilk, egg, and bourbon.
Dunk the chicken pieces, one at a time, into the buttermilk mixture, then dredge in the flour mixture. Use your fingers to massage the flour coating onto the chicken. Place the coated pieces back on the wire rack and rest at least 10 minutes or up to 1 hour.
Heat the peanut oil to 350ºF in a large Dutch oven fitted with a candy/fry thermometer over medium-high heat, about 15 minutes.
Fry the chicken in three batches, rotating the pieces every 3 to 4 minutes, and adjusting the heat as needed to maintain 325ºF. If you manage the heat just right, the exterior of the chicken will be golden brown right as the interior temperature hits 155ºF on an instant-read thermometer, 12 to 15 minutes per batch. Rest the chicken on a wire rack turned upside down on a paper towel-lined pan for at least 5 minutes before serving.