1) Make the sauce base
In a small saucepan or skillet over medium heat, combine orange zest, orange juice, brown sugar, soy sauce, rice vinegar, ketchup (if using), garlic, ginger, and red pepper flakes. Bring to a simmer and cook for 2 to 3 minutes, stirring, until the sugar is dissolved and it smells bright, citrusy, and very “takeout night.”
2) Thicken the sauce
In a small bowl, whisk cornstarch and cold water until smooth. Slowly whisk the slurry into the simmering sauce. Let it bubble for 30 to 60 seconds until glossy and thick enough to coat a spoon. Turn heat to low to keep warm.
Tip: If it tightens up while you fry, whisk in 1 tablespoon water at a time to loosen it back to glossy.
3) Coat the chicken
Pat chicken dry with paper towels. In a bowl, toss chicken with salt, pepper, and the egg until everything is lightly coated.
In a second bowl, mix cornstarch and flour. Add chicken and toss until every piece looks shaggy and well covered. Press the coating on a bit so it sticks.
Optional crunch tip: Let the coated chicken rest for 5 minutes while the oil finishes heating. It helps the coating hydrate and hang on better.
4) Fry until golden
Heat 1 to 1 1/2 inches of oil in a heavy pot or deep skillet to 350°F. You want the oil level safely below halfway up the pot. Fry chicken in batches (do not crowd the pot) for 4 to 6 minutes, turning occasionally, until deep golden and the chicken reaches 165°F internally. Transfer to a wire rack or paper towel lined plate.
Tip: If your oil temp drops, wait a minute before starting the next batch. Crisp edges love steady heat.
5) Toss and finish
When all chicken is fried, add it to a large bowl. Pour warm sauce over and toss quickly until coated. Drizzle with sesame oil if using, then finish with scallions and sesame seeds.
Serve immediately with steamed rice, fried rice, or broccoli. Also acceptable: standing at the counter eating “tester pieces” while the rice finishes.
