Pat chicken pieces dry and season evenly with salt, pepper and garlic powder.
In a bowl whisk eggs with cold water; set aside.
Combine potato starch, flour and baking powder in a separate bowl; mix thoroughly.
Dip each piece into the egg wash, then dredge in the starch-flour mix; press to coat well.
Heat oil in a deep pot to 320°F (160°C). Fry chicken in batches 5–7 minutes until pale golden and cooked through; do not overcrowd.
Remove to a wire rack to rest 8–10 minutes; keep warm.
Increase oil temperature to 375°F (190°C) for the second fry.
Fry chicken a second time 2–3 minutes until deeply golden and extra crispy. Drain on rack; sprinkle a pinch of salt.
Meanwhile, combine gochujang, soy, honey, rice vinegar, brown sugar, garlic, ginger and sesame oil in a saucepan; simmer gently 3–4 minutes until glossy and slightly thickened.
Heat 3 tbsp vegetable oil in a skillet over medium, add the sauce and bring to a bubbling glaze; reduce until spoon coats back of ladle.
Toss the hot fried chicken in the warm sauce in a large bowl until evenly coated, or brush sauce over pieces for a lighter coating.
Transfer to a platter, sprinkle with toasted sesame seeds and sliced scallions. Serve immediately for best crunch.