In a bowl, whisk together buttermilk, hot sauce, salt, black pepper, smoked paprika, garlic powder, and onion powder.

Submerge the chicken thighs in the marinade, cover, and refrigerate for at least 2 hours (or overnight for best results).

In a shallow dish, mix flour, cornstarch, salt, black pepper, smoked paprika, cayenne (if using), garlic powder, and onion powder.

In a separate bowl, whisk together the egg and 1 tablespoon of buttermilk.

Remove the chicken from the buttermilk marinade and let excess drip off.

Dredge each thigh in the flour mixture, then in the egg mixture, and back into the flour mixture, pressing to create a craggy texture.

Heat vegetable oil in a deep skillet or Dutch oven to 350°F (175°C).

Fry chicken for 5-7 minutes per side, or until golden brown and cooked through (internal temperature should reach 165°F / 74°C).

Drain on a wire rack over a baking sheet to keep it crispy.

In a small bowl, mix mayonnaise, minced garlic, lemon juice, salt, and black pepper. Set aside.

Spread garlic aioli on both halves of the toasted brioche bun.

Place a crispy fried chicken thigh on the bottom bun.

Add 2 pickles on top of the chicken.

Add butter lettuce if desired.

Top with the other half of the bun and press gently.