01 - Combine chicken, pickle brine, and hot sauce (if using) in a resealable bag or bowl. Marinate in the refrigerator for at least 1 hour, or up to overnight for maximum flavor penetration.
02 - Pour vegetable oil into a heavy-bottomed pot or deep skillet. Heat to 350°F, maintaining temperature throughout frying for optimal crispiness.
03 - Whisk together flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, kosher salt, and black pepper in a shallow dish until thoroughly combined.
04 - Remove chicken from brine, allowing excess liquid to drip off. Press each piece firmly into the flour mixture, turning to coat all sides completely and shaking off excess.
05 - Fry chicken in batches for 5-7 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to a wire rack or paper towels to drain.
06 - Whisk mayonnaise and Dijon mustard together in a small bowl until smooth and fully incorporated.
07 - Lightly toast the buns until golden. Spread mayo-mustard sauce generously on both cut sides.
08 - Place fried chicken on bottom buns, top with shredded lettuce and pickle slices. Cover with top buns and serve immediately while hot.