01 - In a large mixing bowl, whisk together buttermilk, hot sauce, kosher salt, and black pepper. Submerge chicken thighs in the mixture and marinate for at least 20 minutes, or refrigerate up to overnight for deeper flavor.
02 - Combine all-purpose flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, and salt in a shallow dish. Blend thoroughly to ensure even seasoning.
03 - Remove chicken from marinade, allowing excess to drip off. Dredge each thigh in the seasoned flour mix, pressing firmly to achieve full coverage. Rest coated chicken on a wire rack for 10 minutes to set crust.
04 - Pour vegetable oil into a heavy skillet or Dutch oven to a depth of 1 inch. Heat the oil over medium-high heat to 350°F.
05 - Fry chicken thighs in batches for 5 to 7 minutes per side, turning once, until golden brown and crisp. Internal temperature should reach 165°F. Transfer fried chicken to a clean wire rack to drain.
06 - Carefully combine 1/2 cup hot frying oil with cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt in a heatproof bowl. Whisk until smooth and consistent.
07 - Brush both sides of each fried chicken thigh generously with the Nashville hot sauce to coat evenly.
08 - If desired, spread unsalted butter on the cut sides of brioche buns. Toast in a skillet over medium heat until golden and warmed through.
09 - Layer sauced chicken thighs on the bottom bun, top with dill pickle chips and a robust helping of coleslaw. Cap with the top bun and serve immediately.