1. Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius).
2. In a large bowl, combine the ground beef, egg, onion, milk, bread crumbs, salt, and pepper. Place the mixture into a lightly greased 5×9 inch loaf pan, or form it into a loaf and place it in a lightly greased 9×13 inch baking dish.
3. Bake the meatloaf in the preheated oven for 1 hour.
4. While the meatloaf is baking, make the mashed potatoes. Place the quartered potatoes into a large pot and cover with salted water. Bring to a boil and cook until tender, about 15 minutes. Drain the potatoes and return them to the pot.
5. Add butter and 1/2 cup milk to the potatoes and mash until smooth, creamy, and well-mixed. Add salt and pepper to taste.
6. Once the meatloaf is done, carefully drain any excess fat from the loaf pan or dish. Spread the mashed potatoes over the meatloaf evenly.
7. Sprinkle the shredded cheddar cheese over the top of the mashed potatoes.
8. Place the meatloaf back in the oven and bake for another 15 minutes, or until the cheese is melted and lightly browned.
9. Let stand for a few minutes before slicing. Serve hot and enjoy!
