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 and ketchup. mix well and pour over the meatloaf.