Rinse chicken pieces and pat dry with paper towels. Trim excess fat and, if desired, make 2 small shallow cuts in the thickest parts of breast pieces so they cook evenly.

Make brine

In a large bowl or container, whisk together 4 cups buttermilk, 2 tbs kosher salt, 1 tbs sugar, 1 tbs hot sauce (optional), 1 tsp garlic powder, and 1 tsp black pepper until salt and sugar are dissolved.

Brine the chicken

Submerge the chicken pieces in the buttermilk mixture, cover, and refrigerate at least 4 hours and up to 24 hours. Turn the pieces once or twice during marination so all sides get coated.

For the seasoned flour

About 30 minutes before frying, combine 3 cups all-purpose flour and 1 tbs cornstarch in a shallow bowl or rimmed baking sheet. Add 2 tsp kosher salt, 2 tsp paprika, 1 tsp smoked paprika or cayenne (if using), 1 tsp onion powder, 1 tsp garlic powder, 1 tsp dried thyme, and 1 tsp black pepper. Whisk or sift together until blended. Set the seasoned flour nearby for dredging.

For dredging & frying

Set up dredging station

In a wide shallow bowl, whisk together 2 eggs and 1 cup whole milk until smooth. Place the seasoned flour in another wide shallow dish. Remove the marinated chicken from the refrigerator and let excess buttermilk drip off; do not rinse.

Dredge the chicken

One piece at a time: dredge the chicken in the seasoned flour, pressing to adhere. Shake off excess, dip into the egg-milk mixture, then return to the flour for a second coating, pressing again to form a thick layer. Place coated pieces on a wire rack set over a baking sheet. Let rest 15–20 minutes to set the coating (this helps it stay on during frying).

Heat the oil

Pour about 1 to 1.5 cups neutral oil into a large heavy skillet (cast iron or stainless) so the oil is about 1 to 1.5 inches deep; for more shallow frying you may need to work in batches. Heat the oil over medium-high heat until a deep-fry thermometer reads 325–350°F (163–177°C). Adjust heat to hold temperature between 325–350°F during frying.

Fry the chicken

Working in batches without crowding, carefully lower chicken pieces into hot oil, skin side down first. Fry pieces 12–15 minutes for drumsticks/thighs and 10–12 minutes for breasts depending on size, turning occasionally so all sides brown evenly; maintain oil temperature between 325–350°F. Internal temperature should reach 165°F (74°C) measured at the thickest part away from bone. If coating browns too quickly, lower heat slightly.

Drain and rest

Using tongs, transfer cooked chicken to a wire rack set over a sheet pan to drain and stay crisp. Sprinkle lightly with fine salt and freshly ground black pepper while hot. Let rest 5–10 minutes before serving to allow juices to redistribute and coating to crisp further.

Finishing

Serve the buttermilk fried chicken hot or at warm room temperature with preferred sides (coleslaw, biscuits, mashed potatoes). Leftovers can be stored uncovered in the fridge for up to 2 days and reheated in a 375°F oven on a rack to restore crispness.