01 - In a large mixing bowl, combine buttermilk, hot sauce, kosher salt, and black pepper. Submerge chicken thighs in the marinade and refrigerate for at least 20 minutes or up to 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 from the marinade and allow excess liquid to drip off. Coat each thigh in the seasoned flour mixture, pressing firmly to ensure full coverage. Place on a wire rack and let rest for 10 minutes to set the coating.
04 - Fill a heavy skillet or Dutch oven with about 1 inch of vegetable oil. Heat oil to 350°F (use a thermometer to maintain temperature).
05 - Fry chicken thighs in hot oil in batches, 5 to 7 minutes per side, until golden brown, crisp, and internal temperature reaches 165°F. Transfer fried chicken to a wire rack to drain excess oil.
06 - In a bowl, combine 1/2 cup of hot frying oil with cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt. Whisk until smooth. Brush sauce liberally over both sides of fried chicken thighs.
07 - Spread unsalted butter on cut sides of brioche buns and toast in a skillet over medium heat until golden brown.
08 - Place a hot sauced chicken thigh on the bottom half of each bun. Top with dill pickle chips and a generous scoop of coleslaw. Close sandwiches with the top bun and serve promptly.