In a large bowl, combine the beef, egg, onion, milk and bread OR cracker crumbs. Season with salt and pepper to taste and place in a lightly greased 9x5-inch loaf pan, or form into a loaf and place in a lightly greased 9x13-inch baking dish.
In a separate small bowl, combine the brown sugar, mustard (if you want mustard) and ketchup. Mix well and pour over the meatloaf.