01 - In a large bowl, combine buttermilk, dill, garlic powder, onion powder, salt, and black pepper. Add chicken breasts, turning to coat thoroughly. Cover and marinate in the refrigerator for at least 30 minutes, or up to 4 hours for optimal flavor infusion.
02 - In a shallow dish, whisk together flour, cornstarch, smoked paprika, salt, and black pepper until evenly distributed.
03 - Remove chicken from marinade, allowing excess liquid to drip off. Press each piece firmly into the flour mixture to ensure complete coating. Arrange coated pieces on a tray and let rest for 5 minutes to set the breading.
04 - Heat oil in a deep fryer or large skillet to 350°F. Fry chicken breasts in batches for 4–5 minutes per side until golden brown and cooked through to an internal temperature of 165°F. Transfer to paper towels to drain excess oil.
05 - In a small bowl, whisk together mayonnaise, fresh dill, lemon juice, Dijon mustard, garlic powder, salt, and pepper until smooth and well combined.
06 - Lightly toast the brioche buns. Spread dill mayo generously on both halves. Layer shredded lettuce and pickles on the bottom bun, place the crispy chicken on top, add tomato slices if desired, and crown with the top bun.
07 - Serve immediately while chicken is hot and breading remains crisp for best texture and flavor.