In a bowl whisk together the egg white, all-purpose flour, cornstarch, baking powder, and ice-cold water until just combined to form a batter; a few small lumps are fine.
Toss the chicken pieces into the batter, ensuring each piece is well coated.
Heat about 2 inches of oil in a wok or deep skillet over medium-high heat until hot (ready for deep-frying).
Carefully deep-fry the battered chicken in batches until golden brown and cooked through, then transfer to a plate lined with paper towels to drain excess oil.
Wipe out the wok or skillet, add 1 tablespoon oil and heat over medium. Sauté the minced garlic until fragrant, about 30 seconds.
Add the fried chicken to the pan, then pour in the Thai sweet chili sauce, lime juice, and a pinch of salt; toss or stir to coat the chicken evenly in the sauce.
Transfer to a serving dish and sprinkle with white sesame seeds and chopped cilantro leaves, then serve immediately.