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 at least 2 hours or overnight for maximum flavor penetration.
02 - Combine flour, cornstarch, paprika, baking powder, cayenne, salt, and black pepper in a shallow dish until evenly blended.
03 - Pour vegetable oil into a deep fryer or heavy-bottomed pot. Heat to 350°F, maintaining consistent temperature throughout frying.
04 - Remove chicken from marinade, allowing excess liquid to drip off. Press each piece firmly into flour mixture, turning to coat thoroughly and creating a thick, craggy exterior.
05 - Lower chicken pieces carefully into hot oil. Fry for 6 to 8 minutes, turning once halfway through, until golden brown and internal temperature reaches 165°F. Transfer to wire rack to drain.
06 - Lightly toast burger buns until golden and warm.
07 - Stir together mayonnaise and hot sauce for spicy mayonnaise, if desired.
08 - Spread mayonnaise on bottom buns. Layer lettuce, fried chicken, tomato slices, and pickles. Crown with top buns and serve immediately.