Preheat the oven to 350 degrees and lightly grease a loaf pan.
In a large bowl, combine the ground beef, diced sweet onion, chopped parsley, breadcrumbs, egg, milk, salt, and black pepper. Mix with your hands until the ingredients are evenly distributed.
Press the mixture into the prepared loaf pan and smooth the top.
Spread the ketchup evenly over the surface of the meatloaf.
Bake for 55 to 60 minutes until the internal temperature reaches 160 degrees.
Remove from the oven and let the meatloaf rest for 10 minutes before slicing.