01 - In a large bowl, whisk together buttermilk, hot sauce, kosher salt, and black pepper. Add chicken thighs, ensuring they are fully coated. Cover and marinate in the refrigerator for at least 20 minutes or up to overnight.
02 - Combine flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, and salt in a shallow bowl. Stir to blend thoroughly.
03 - Remove chicken from marinade, letting excess liquid drip off. Dredge each thigh in the flour mixture, pressing firmly to adhere. Transfer prepared pieces to 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.
05 - Working in batches, fry chicken thighs for 5–7 minutes per side, until golden brown and cooked through to 165°F internal temperature. Transfer fried chicken to a clean wire rack.
06 - In a heatproof bowl, combine cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt. Gently ladle in 1/2 cup hot frying oil and whisk until smooth. Generously brush both sides of each fried chicken thigh with sauce.
07 - Spread unsalted butter on the cut sides of brioche buns. Toast in a skillet over medium heat until golden and crisp.
08 - Layer Nashville hot chicken thighs onto the bun bottoms. Top with dill pickle chips and a generous portion of coleslaw. Cap each with the top bun. Serve promptly while hot.