Creating Sweet and Sour Meatballs is straightforward by following these easy steps:

1. Preheat Oven: Set your oven to 400°F (200°C).
2. Prepare Meatball Mixture: In a large bowl, combine ground beef, breadcrumbs, egg, onion, garlic powder, salt, and pepper. Mix until just combined.
3. Shape Meatballs: Form small meatballs (about 1 inch in diameter) and place them on a baking sheet, lined with parchment paper.
4. Bake Meatballs: Bake in the preheated oven for 20 minutes, or until cooked through.
5. Make the Sauce: While the meatballs are baking, whisk together ketchup, apple cider vinegar, brown sugar, and soy sauce in a saucepan over medium heat.
6. Thicken the Sauce (Optional): If you prefer a thicker sauce, mix cornstarch and water in a small bowl until smooth. Add this mixture to the sauce, stirring until it thickens slightly.
7. Combine and Serve: Once the meatballs are done, add them to the sauce, ensuring they are well-coated. Serve hot, garnished with green onions if desired.

These simple steps guide you through what could be your new favorite dish with ease!