In a large bowl, combine buttermilk, pickle juice, sriracha, paprika, white pepper, garlic powder, salt, and egg.
Add chicken fillets, mix well, and marinate for at least 2 hours (or overnight for best results).
In a shallow bowl, mix flour, rice flour, corn flour, paprika, white pepper, garlic powder, and salt.
Add 1 tbsp of buttermilk from the marinade and gently mix with your fingers to create a crumbly coating texture.
Dredge each piece of marinated chicken in the coating mixture, pressing firmly to help the crumbs stick.
Heat oil in a deep pan over medium heat (around 170–180°C).
Fry chicken in batches for 5–6 minutes per side, until golden and crispy.
Transfer to a wire rack to drain excess oil.
In a small saucepan, melt 1 tbsp butter and sauté garlic until fragrant.
Add soy sauce, sesame oil, ketchup, chili flakes, honey, and water.
Simmer for 2–3 minutes, then whisk in 1 tbsp more butter to finish.
Toast your brioche buns lightly for a golden, buttery finish.
Spread a layer of American burger sauce on the bottom bun, then add pickle slices.
Toss the fried chicken pieces in the honey butter sauce until evenly coated.
Place the saucy chicken on the buns, top with more pickles if you like, and cover with the top bun.
Serve immediately while warm and crispy.