In a bowl, whisk together flour, cornstarch, baking powder, salt, and pepper. Add cold water slowly until you get a thick, smooth batter.
1 cup all-purpose flour, ½ cup cornstarch, 1 teaspoon baking powder, Salt and pepper to taste, ¾ cup cold water
Dip each chicken piece into the batter, fully coating it.
1 pound chicken breast
Heat oil in a deep pot or pan to 350°F (175°C). Fry chicken balls in batches for 4–5 minutes, or until golden and fully cooked inside. Drain on a paper towel-lined plate.
Oil for deep frying
In a saucepan, combine ketchup, vinegar, sugar, soy sauce, and pineapple juice. Bring to a simmer. Stir in cornstarch slurry and cook until thickened, about 2–3 minutes.
½ cup ketchup, ¼ cup white vinegar, 1 tbsp soy sauce, ¼ cup granulated sugar, ¼ cup pineapple juice, 1 tablespoon cornstarch
Serve chicken balls hot with the sauce on the side or pour it over the top. Garnish with sesame seeds or chopped scallions if desired.