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 refrigerate for at least 30 minutes, or up to 4 hours for optimal flavor infusion.
02 - In a shallow dish, whisk together flour, cornstarch, paprika, salt, and black pepper until well combined.
03 - Remove chicken from marinade, allowing excess liquid to drip off. Press each piece firmly into the flour mixture to ensure complete coating. Arrange breaded chicken on a tray and let rest for 5 minutes to set the coating.
04 - Heat oil in a deep fryer or large skillet to 350°F. Working in batches, fry chicken breasts for 4–5 minutes per side until golden brown and cooked through (internal temperature reaches 165°F). Transfer to paper towels to drain excess oil.
05 - In a small bowl, whisk together mayonnaise, dill, lemon juice, Dijon mustard, garlic powder, salt, and pepper until smooth and evenly blended.
06 - Lightly toast brioche buns until golden. Spread dill mayo generously on both halves of each bun.
07 - Layer shredded lettuce and pickles on the bottom bun. Place crispy chicken on top, followed by optional tomato slices. Cover with top bun and serve immediately while hot and crispy.