Put ground meat into a mixing bowl. Add egg, breadcrumbs, cornstarch, light soy sauce, sesame oil, salt, white pepper, and garlic powder (optional). Mix until well combined.
Divide the mixture into 20-22 equal portions (about 1 heaping tablespoon each). Use your hands to shape each portion into a ball.
Bake the meatballs
Preheat the oven to 350ºF (180ºC) or 320ºF (160ºC) for a fan-assisted oven.
Arrange the meatballs on a baking dish (line it with parchment paper if it isn't non-stick). Place the dish over the middle rack of the oven. Leave to bake for about 12 minutes (see note 2).
Cook the sauce
In a bowl, combine tomato ketchup, black rice vinegar, sugar, light soy sauce, cornstarch, white pepper, and water. Stir until smooth and lump-free.
Pour the mixture into a skillet. Cook over low heat while stirring with a spatula constantly. Once the sauce is nearly at the desired consistency, add the baked meatballs.
Turn off the heat and gently stir the meatballs until they are evenly coated in the sauce. Optionally, sprinkle toasted sesame seeds over before serving.
Notes
1. For a tender texture and richer taste, choose ground meat that has a high content of fat.2. The cooking time may vary slightly depending on your oven’s performance. If unsure, check one meatball with a kitchen thermometer. The reading should be above 160ºF (71ºC).