01 - Combine buttermilk, hot sauce, kosher salt, and black pepper in a large mixing bowl. Submerge chicken thighs and marinate for at least 20 minutes, or refrigerate overnight for optimal tenderness.
02 - In a shallow dish, thoroughly mix all-purpose flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, and salt.
03 - Remove chicken thighs from marinade, allowing excess liquid to drip off. Dredge each piece in the flour mixture, pressing firmly to ensure a robust coating. Set coated pieces on a wire rack and let rest for 10 minutes.
04 - Pour vegetable oil into a heavy skillet or Dutch oven to a depth of approximately 1 inch. Heat the oil to 350°F (use a thermometer to monitor temperature).
05 - Working in batches, carefully place coated chicken into hot oil. Fry 5 to 7 minutes per side, until golden brown and the internal temperature reaches 165°F. Transfer fried chicken to a wire rack to drain.
06 - In a medium bowl, whisk together 1/2 cup of hot frying oil, cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt until fully blended. Generously brush sauce onto both sides of each fried chicken piece.
07 - If desired, lightly spread unsalted butter on the cut sides of brioche buns and toast in a skillet over medium heat until golden.
08 - Layer each bun bottom with a piece of sauced fried chicken, followed by dill pickle chips and a generous scoop of coleslaw. Cap with the top bun and serve immediately.