Preheat oven to 375oF (Gas Mark 5) spray an 8 × 4 - (9 × 5 - 2lb loaf tin) inch loaf pan with nonstick cooking spray.
Mix together beef,diced onion,salt,pepper,breadcrumbs,milk,and Ketchup in a large bowl until thoroughly combined.Transfer mixture to prepared loaf pan.
Bake the meatloaf for 40 minutes on the middle rack of oven.
Open oven and spoon Ketchup in an even layer over the top of meatloaf.Bake for 15 - 20 minutes longer,until center of loaf reaches 160oF.
Check to see that meatloaf is done.Remove from oven or add time as needed.
Allow meatloaf to rest for 10 - 15 minutes before serving.
