Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line with foil.

In a large mixing bowl, combine the ground beef, chopped onion, eggs, and milk. Stir in breadcrumbs, garlic, ketchup, parsley, Worcestershire sauce, salt, pepper, and Italian seasoning until just combined.

Transfer mixture to the prepared pan, shaping it into a loaf with an even thickness.

In a small bowl, mix brown sugar, vinegar, and a bit more ketchup for glaze. Brush half onto the meatloaf.

Bake for 45 minutes, then brush remaining glaze on top and bake for an additional 15 to 30 minutes, until internal temperature reaches 160°F (71°C).

Let the meatloaf rest for 10 to 15 minutes before slicing and serving.