Dry Brine the Chicken:Sprinkle kosher salt evenly over the chicken thighs. Place them on a wire rack and refrigerate uncovered overnight to draw out moisture and deepen flavor.
Make the Marinade:In a large bowl, whisk together eggs, buttermilk, hot sauce, and pickle juice. Submerge the chicken thighs completely, cover with plastic wrap, and refrigerate for at least 2 hours.
Prepare the Dredge:Mix flour, salt, and cracked black pepper in a large bowl. Add a few tablespoons of the marinade to form small clumps in the flour—these will fry up into crunchy bits.
Dredge the Chicken:Remove chicken from the marinade and let excess drip off. Coat each thigh in the flour mixture, pressing firmly to ensure full coverage. No bare spots.
Fry the Chicken:Heat oil or lard to 325°F in a large Dutch oven. Fry the chicken in small batches for 15–18 minutes or until internal temperature reaches 165°F. When thighs float to the surface, begin checking for doneness. Let rest on a wire rack.
Make the Spicy Oil:In a heatproof bowl, combine cayenne pepper, onion powder, smoked paprika, garlic powder, salt, MSG (if using), brown sugar, and crushed Thai chilies. Carefully pour 1½ cups of HOT frying oil over the spices. The oil must be hot to bloom the spices and create that signature flavor. Whisk until smooth and deep red.Caution: Pepper fumes can cause irritation. Work in a well-ventilated area.
Coat the Chicken:Dunk each fried piece in the spicy oil until fully coated. Place on a wire rack to rest for 1–2 minutes to set the coating.
Assemble the Sandwich:Toast brioche buns until golden. Spread mayo on the bottom bun, add one piece of hot chicken, top with pickles, and a spoonful of slaw if desired. Serve immediately.