01 - Combine chicken, pickle brine, and hot sauce in a resealable bag or bowl. Refrigerate for at least 1 hour, preferably overnight for maximum flavor penetration.
02 - Whisk together flour, cornstarch, paprika, garlic powder, onion powder, cayenne, salt, and pepper in a shallow dish until evenly combined.
03 - Pour vegetable oil into a heavy-bottomed pot or deep skillet. Heat to 350°F, maintaining temperature throughout frying process.
04 - Remove chicken from brine, allowing excess liquid to drip off. Press firmly into flour mixture, turning to coat all sides completely.
05 - Fry chicken pieces in batches for 5-7 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to wire rack to drain.
06 - Combine mayonnaise and Dijon mustard in a small bowl, stirring until smooth and well incorporated.
07 - Lightly toast bun halves until golden. Spread prepared mayo-mustard sauce on both top and bottom buns.
08 - Place fried chicken on bottom bun, layer with shredded lettuce and pickle slices. Top with remaining bun and serve immediately while hot.