Prep the chicken: Pat the chicken dry.
If using breasts, slice them into thinner cutlets for even cooking. Lightly pound to an even thickness if needed.
Marinate: In a bowl, combine buttermilk (or yogurt), soy sauce, garlic, ginger, gochugaru, and a pinch of salt. Add the chicken, coat well, and refrigerate for at least 30 minutes (up to 8 hours for deeper flavor).
Make the slaw: In a large bowl, whisk mayo, rice vinegar, sesame oil, sugar, and a pinch of salt.
Toss in cabbage, carrot, scallions, and sesame seeds. Taste and adjust seasoning. Chill until ready to build.
Whisk the sauce: Stir together gochujang, soy sauce, honey, rice vinegar, sesame oil, garlic, ginger, and water.
Set aside. It should be glossy and pourable; add a splash more water if too thick.
Mix the dredge: In a shallow dish, combine flour, potato starch, baking powder, salt, and pepper. This blend gives lift and a crisp bite.
Dredge the chicken: Remove a piece from the marinade, let excess drip off, and press into the dredge.
Pack the coating on so it adheres. Place on a wire rack while you finish the rest.
Heat the oil: Pour 1/2 inch of neutral oil into a heavy skillet and heat to about 350°F (175°C). If you don’t have a thermometer, a small pinch of flour should sizzle on contact.
Fry in batches: Carefully lay in the chicken without crowding.
Fry 3–4 minutes per side, until deeply golden and the internal temp reaches 165°F (74°C). Transfer to a clean rack to stay crisp.
Warm the sauce: In a small pan over low heat, simmer the sauce for 1–2 minutes until slightly thickened and shiny. Don’t boil hard; you want it sticky, not burnt.
Toss or drizzle: For saucy chicken, gently toss the fried pieces in the warm sauce to coat.
For extra-crispy texture, drizzle a little sauce over the chicken on the bun and serve more on the side.
Toast the buns: Butter the cut sides and toast in a skillet until golden. This small step keeps the buns from getting soggy.
Assemble: Bun base, pickles if using, sauced chicken, a generous pile of slaw, then the top bun. Press gently to set everything in place.
Serve: Eat right away while the chicken is hot and the slaw is crisp.
A few extra sesame seeds on top look great.