01 - Whisk together buttermilk, hot sauce, garlic powder, onion powder, salt, and pepper in a large bowl. Submerge chicken thighs completely, cover, and refrigerate for 2 hours to overnight.
02 - Combine flour, cornstarch, paprika, baking powder, cayenne, salt, and black pepper in a shallow dish until evenly distributed.
03 - Pour vegetable oil into deep fryer or heavy-bottomed pot. Heat to 350°F, maintaining temperature throughout frying.
04 - Lift chicken from marinade, allowing excess liquid to drip off. Press each piece firmly into flour mixture, ensuring thick, craggy coating adheres to all surfaces.
05 - Lower coated pieces carefully into hot oil. Fry 6 to 8 minutes, turning once halfway through, until golden brown with internal temperature reaching 165°F. Transfer to wire rack to drain.
06 - Lightly toast cut sides of burger buns until golden and warm.
07 - Stir together mayonnaise and hot sauce until smooth for spicy mayo variation.
08 - Spread mayonnaise on toasted bottom buns. Layer lettuce, fried chicken, tomato slices, and pickles. Crown with top buns and serve immediately.