01 - In a large mixing bowl, whisk together buttermilk, hot sauce, salt, and black pepper. Submerge chicken thighs and refrigerate for at least 20 minutes or up to overnight for optimal tenderness.
02 - In a shallow dish, blend flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, and salt until evenly incorporated.
03 - Lift chicken from marinade, allowing excess liquid to drip away. Dredge each thigh firmly in the seasoned flour mixture, pressing to ensure a thorough coating. Arrange 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 1 inch. Heat oil to 350°F (175°C), monitoring temperature for consistency.
05 - In batches, fry chicken thighs for 5 to 7 minutes per side until golden and crispy, ensuring the internal temperature reaches 165°F (74°C). Transfer to a clean wire rack to drain.
06 - In a medium bowl, combine 1/2 cup of the hot frying oil with cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt. Whisk until the mixture is smooth and fully blended.
07 - Generously brush both sides of the fried chicken with the prepared Nashville hot sauce while the chicken is still hot.
08 - Optional: Spread unsalted butter on the cut sides of brioche buns and toast in a skillet until lightly golden and crisp.
09 - Arrange one sauced chicken thigh on each bottom bun. Top with dill pickle chips and a generous scoop of coleslaw. Set the top bun in place and serve immediately for best texture.