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.