Place the chicken pieces in a bowl. Add soy sauce, ginger-garlic paste, white pepper and the marinade salt. Mix, cover and refrigerate for 15–30 minutes. This step adds flavor but can be skipped if short on time.

Prepare batter

In a medium bowl, whisk together cornstarch, all-purpose flour, baking powder, salt and black pepper. Beat the egg and stir into the dry mixture. Add 1/4 cup cold water and stir until a smooth but slightly thick batter forms. If too thick, add up to 1 tablespoon more water. The batter should coat pieces but not be runny.

Toss the marinated (or plain) chicken pieces into the batter, ensuring each piece is well coated. Let rest 5 minutes so coating adheres.

Frying Chicken

Heat about 1 to 1 1/2 inches of oil in a deep skillet or pot over medium-high heat to 350°F (175°C). If you don't have a thermometer, test by dropping a small bit of batter into the oil — it should sizzle and rise to the surface promptly.

Carefully add chicken pieces in a single layer (work in batches to avoid overcrowding). Fry 4–6 minutes per batch, turning occasionally, until golden brown and cooked through. Internal temperature should reach 165°F (74°C).

Use a slotted spoon to transfer fried chicken to a wire rack or paper towel–lined plate to drain. Repeat with remaining chicken. Keep pieces warm in a low oven (200°F / 95°C) if desired.

Sauce & Vegetables

In a small bowl, combine ketchup, soy sauce, rice vinegar, chili sauce, sugar, 1/2 cup water (or stock), and the 1 teaspoon cornstarch reserved for the slurry mixed with 1 tablespoon cold water. Stir until smooth and set aside.

Wipe out most of the frying oil from the skillet, leaving about 1–2 tablespoons for stir-frying. Heat the skillet over medium-high heat until hot.

Add minced garlic, sliced ginger and the white parts of the green onions. Stir-fry 20–30 seconds until fragrant, being careful not to burn the garlic.

Add dried red chilies (if using), chopped red bell pepper and onion. Stir-fry 1.5–2 minutes until vegetables begin to soften but remain crisp-tender.

Pour the prepared sauce mixture into the skillet. Bring to a simmer while stirring; the cornstarch slurry will thicken the sauce in about 30–60 seconds. Taste and adjust seasoning with the 1/4 teaspoon salt and freshly ground black pepper as needed.

If the sauce becomes too thick, add up to 1–2 tablespoons water to reach desired consistency.

Finishing & Serve

Add the fried chicken pieces to the sauce and toss gently to coat each piece evenly. Cook together 1–2 minutes to reheat chicken and let the sauce cling.

Turn off heat and sprinkle with sliced green onion tops and sesame seeds if using. Give one gentle toss.

Transfer to a serving platter and serve immediately with steamed rice or fried rice.