Step 1: Prepare the Meatballs

1. Preheat the Oven: Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper or lightly grease it to prevent the meatballs from sticking.
2. Combine the Ingredients: In a large mixing bowl, combine the ground beef, breadcrumbs, milk, egg, chopped onion, minced garlic, soy sauce, salt, and pepper. Use clean hands or a spoon to mix everything together until just combined, being careful not to overmix as this can make the meatballs tough.
3. Form the Meatballs: Scoop out about 1 tablespoon of the meat mixture and roll it between your hands to form a small ball. Place the meatball on the prepared baking sheet, and repeat with the remaining mixture, arranging the meatballs in a single layer. You should have about 30 meatballs, depending on the size.
4. Bake the Meatballs: Bake the meatballs in the preheated oven for 15-18 minutes, or until they’re cooked through and slightly browned on the outside. Baking the meatballs rather than frying them is not only healthier but also much easier, as you don’t need to stand by the stove.

Step 2: Make the Sweet and Sour Sauce

1. Mix the Sauce Ingredients: While the meatballs are baking, prepare the sweet and sour sauce. In a medium saucepan, combine the ketchup, brown sugar, vinegar, soy sauce, Worcestershire sauce (if using), and pineapple juice. Stir well to combine and dissolve the sugar.
2. Bring to a Simmer: Place the saucepan over medium heat and bring the sauce to a simmer, stirring occasionally. Once the sauce begins to bubble, reduce the heat to low and let it cook for 5-7 minutes to allow the flavors to meld.
3. Thicken the Sauce: In a small bowl, mix the cornstarch with water to create a slurry, then add it to the sauce. Stir constantly for 1-2 minutes, until the sauce thickens to a glossy, sticky consistency. Taste and adjust the sauce, adding more sugar if you prefer it sweeter, or a little extra vinegar for more tang.

Step 3: Combine the Meatballs and Sauce

1. Add the Meatballs to the Sauce: Once the meatballs are done baking, carefully transfer them to the saucepan with the sauce. Gently toss to coat each meatball in the sweet and sour sauce, ensuring they’re fully covered.
2. Simmer for Extra Flavor: Allow the meatballs to simmer in the sauce for another 5-10 minutes on low heat. This step helps the meatballs absorb the sauce, making them even more flavorful.
3. Add Optional Pineapple Chunks: For extra sweetness and texture, add fresh or canned pineapple chunks to the saucepan during the last few minutes of simmering. The pineapple adds a burst of tropical flavor that pairs perfectly with the tangy sauce.

Step 4: Garnish and Serve

1. Garnish with Green Onions and Sesame Seeds: Transfer the sweet and sour meatballs to a serving dish and garnish with sliced green onions and sesame seeds for a pop of color and flavor.
2. Serve Hot: Serve the meatballs hot, with additional sauce on the side for dipping. They’re perfect on their own as an appetizer, or you can serve them over steamed rice or noodles for a complete meal.