01 - In a bowl or resealable bag, combine chicken, pickle brine, and hot sauce (if using). Marinate in the refrigerator for at least 1 hour and up to overnight.
02 - Heat oil in a heavy-bottomed pot or deep skillet to 350°F (175°C).
03 - In a shallow dish, whisk together flour, cornstarch, paprika, garlic powder, onion powder, cayenne, salt, and pepper.
04 - Remove chicken from brine, letting excess drip off. Dredge thoroughly in the flour mixture to coat on all sides.
05 - Fry chicken pieces in batches, 5–7 minutes per side, until golden brown and cooked through (internal temperature should reach 165°F/74°C). Drain on a wire rack or paper towels.
06 - Mix mayonnaise and Dijon mustard in a small bowl.
07 - Lightly toast the buns. Spread the mayo-mustard sauce on both sides.
08 - Layer fried chicken, lettuce, and pickle slices onto the buns. Top with remaining bun halves. Serve immediately.