Preheat oven to 350 degrees F (175 degrees C).
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 5×9 inch loaf pan, OR form into a loaf and place in a lightly greased 9×13 inch baking dish.
In a separate small bowl, combine the brown sugar, mustard and ketchup. Mix well and pour over the meatloaf.
Bake at 350 degrees F (175 degrees C) for 1 hour.