01 -
Preheat oven to 350°F (175°C). Lightly grease a 9x5-inch loaf pan.
02 -
Combine ground beef, chopped onion, milk, bread crumbs, and egg in a large bowl. Season with salt and pepper to taste.
03 -
Transfer mixture into prepared loaf pan, pressing gently to form an even loaf.
04 -
Mix ketchup, brown sugar, and mustard in a small bowl until well combined. Pour over meatloaf and spread evenly across the top.
05 -
Bake in preheated oven for 1 hour, or until internal temperature reaches 160°F and meat is no longer pink in center.
06 -
Allow to rest for 5 minutes before slicing and serving hot.