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 in half. Sprinkle the chicken on all sides with half of the spice mixture, then refrigerate, uncovered, for at least 4 hours or up to overnight.
When you're ready to cook, remove the chicken from the refrigerator. Whisk together the flour, cornstarch, and the remaining spice mixture in a large bowl. In another bowl, whisk together the buttermilk, egg, and bourbon.
One piece at a time, dunk the chicken pieces 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 at room temperature.
Meanwhile, heat the peanut oil to 350ºF in a large Dutch oven over medium-high heat, about 15 minutes. Line a rimmed baking sheet with paper towels and place a wire cooling rack upside down on the paper towels.
When the oil is hot, fry the chicken in three batches, rotating the pieces every 3 to 4 minutes, until the chicken is golden brown and its interior temperature is 155°F, about 10 minutes. (It helps to fry the white meat pieces together in their own batches and the dark meat together in their own batches.) Adjust the heat as needed to maintain 325°F. Rest the chicken on the prepared rack for at least 5 minutes before serving. The chicken is equally good at room temperature as it is hot, so don’t worry about keeping it warm between batches.