Prep the chicken: If using thighs, trim excess fat and gently pound to an even 1/4-inch thickness so they cook quickly and evenly.
Marinate: In a bowl, whisk together buttermilk, minced garlic, lime juice, fish sauce, sugar, and white pepper. Add the chicken, cover, and refrigerate 20–30 minutes (or up to 4 hours for deeper flavor).
Make the slaw: In a separate bowl, toss cabbage, carrot, cilantro, lime juice, sugar, and a pinch of salt. Let sit while the chicken marinates so the flavors mingle and soften the crunch.
Coat the chicken: In a plate or shallow bowl, combine rice flour, cornstarch, baking powder, paprika, and salt. Remove chicken from marinade, pat dry, and lightly shake off excess liquid. Dredge each piece in the coating, pressing gently to ensure a crusty layer sticks.
Heat the oil: In a heavy pot or skillet, heat oil to 350°F (175°C). Use a thermometer to monitor temperature; keep it steady for even frying.
Fry until crisp and cooked through: Fry in batches 3–4 minutes per side, until golden brown and the internal temperature reaches 165°F (74°C). Transfer to a rack or paper-towel-lined plate to drain.
Make the sauce: Whisk mayonnaise and Thai sweet chili sauce together. Taste and adjust the ratio if you like a milder or bolder heat.
Toast the buns: Lightly butter and toast the buns in a skillet or on a hot griddle for 1–2 minutes, until golden and just crisp at the edges.
Assemble: Spread a thin layer of sauce on both bun halves. Layer the bottom bun with crispy chicken, a generous heap of slaw, cucumber slices if using, and a few cilantro leaves. Top with the sauced bun top and press gently to set.
Notes
Thai Fried Chicken Sandwich: Crispy, Tangy, and Totally Addictive — a Thai-inspired fried chicken sandwich with a light crackly crust, juicy chicken, and a bright lime-cilantro slaw finished with a creamy Thai sweet chili sauce.
