Preheat oven to 375°F (190°C). In a large bowl, combine ground beef, breadcrumbs, milk, egg, chopped onion, salt, and pepper. Mix gently until just combined, being careful not to overwork the mixture. Shape it into a loaf and place it in a baking dish.

In a small bowl, whisk together ketchup, brown sugar, and Worcestershire sauce to make the glaze. Spread half of it evenly over the meatloaf and bake for 45 minutes.

Remove from the oven, top with the remaining glaze, and bake another 15 minutes, or until the internal temperature reaches 160°F (71°C). Let the meatloaf rest for 10 minutes before slicing and serving.