Preheat the oven to 350 degrees F (177 degrees C).
In a large bowl, combine all ingredients except the beef and ketchup, and mix. Then add meat and mix until fully incorporated. Avoid overmixing.
Transfer the mixture into a large baking dish and form into a loaf shape. Bake for 30 minutes.
Spread the ketchup on top of the meatloaf (if using). Return to the oven and bake for 25-45 more minutes, until cooked through and the internal temperature reaches 160 degrees F (71 degrees C). (Time will vary depending on thickness of the loaf.) For best results, use a probe thermometer, which will beep when it's done so you don't have to keep checking.
Rest for 10 minutes before slicing. The internal temperature should rise another 5 degrees F. Slice carefully using a serrated bread knife (not a chef's knife).