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 up to overnight in the refrigerator.
02 - In a shallow dish, blend all-purpose flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, and salt until evenly mixed.
03 - Remove chicken from marinade, allowing excess to drip off. Dredge each thigh in the flour mixture, pressing firmly to ensure even coating. Arrange dredged chicken on a wire rack and let stand for 10 minutes.
04 - Pour vegetable oil into a heavy skillet or Dutch oven to a depth of 1 inch and heat to 350°F. Confirm temperature with a thermometer.
05 - Fry chicken thighs in hot oil, working in batches if needed, for 5 to 7 minutes per side until golden brown and crisp. Check that internal temperature reaches 165°F. Transfer fried chicken to a clean wire rack to drain.
06 - In a medium bowl, vigorously whisk 1/2 cup hot frying oil with cayenne pepper, brown sugar, chili powder, smoked paprika, garlic powder, and salt until emulsified and smooth. Brush mixture generously onto both sides of each fried chicken thigh.
07 - If desired, spread butter on the cut sides of the brioche buns and toast in a skillet over medium heat until golden brown.
08 - Arrange sauced fried chicken on the bottom half of each bun. Top each with dill pickle chips and a generous serving of coleslaw. Place the top bun and serve immediately.