Preheat the oven to 400°F and line a baking sheet with parchment paper.
Heat a small skillet over medium heat and sauté the diced onion with a pinch of salt until soft and translucent, about 4–5 minutes, then add the garlic and cook for 30 seconds more before removing from heat to cool slightly.
In a large bowl, whisk together the eggs and milk until smooth.
Add the ground beef, ground pork, breadcrumbs, sautéed onion mixture, ketchup, Worcestershire sauce, salt, and pepper to the bowl.
Gently mix with your hands just until combined, being careful not to overmix.
Scoop and roll the mixture into 1½-inch meatballs and place them evenly spaced on the prepared baking sheet.
In a small bowl, stir together the ketchup, brown sugar, and Worcestershire sauce for the glaze.
Brush or spoon the glaze over each meatball.
Bake for 20–22 minutes, or until the internal temperature reaches 160°F.
Let rest for 5 minutes before serving.