Step 1: Prepare the Chicken
If the chicken breasts are thick, slice them in half horizontally or pound them with a meat mallet for even cooking.
In a bowl, mix buttermilk, salt, black pepper, paprika, garlic powder, onion powder, and cayenne.
Submerge the chicken in the buttermilk mixture and let it marinate for at least 1 hour (or overnight for best results).
Step 2: Prepare the Breading
In a shallow dish, whisk together flour, cornstarch, salt, black pepper, paprika, garlic powder, onion powder, and cayenne.
In another bowl, whisk together the egg and 2 tablespoons of buttermilk.
Step 3: Coat the Chicken
Remove the chicken from the marinade, letting excess buttermilk drip off.
Dredge the chicken in the flour mixture, then dip it into the egg mixture, and coat it again in the flour mixture, pressing firmly for a thick, crispy crust.
Place coated chicken on a wire rack and let it rest for 10 minutes.
Step 4: Fry the Chicken
Heat oil in a deep fryer or large skillet to 350°F (175°C).
Fry each chicken breast for 3-4 minutes per side or until golden brown and cooked through (internal temperature of 165°F (74°C)).
Transfer to a wire rack to drain excess oil.
Step 5: Make the Sauce
In a small bowl, mix mayonnaise, Dijon mustard, honey, lemon juice, garlic powder, and smoked paprika.
Step 6: Assemble the Sandwich
Butter the brioche buns and toast them in a skillet until golden.
Spread the sauce on both halves of the bun.
Add lettuce, pickles, and the crispy chicken breast.
Top with the other half of the bun and serve hot!