In a large mixing bowl, combine ground beef, breadcrumbs, shredded cheese, diced onions, minced garlic, egg, salt, and pepper. Mix gently until evenly combined.

Transfer the mixture to a baking pan, shaping it into a neat loaf approximately 2 inches tall. Spread ketchup or BBQ sauce over the top.

Preheat the oven to 350°F (175°C). Bake the meatloaf for 50-60 minutes, checking internal temperature with a meat thermometer to ensure it reaches 160°F.

Meanwhile, peel and chop the potatoes into even chunks. Place in a pot, cover with salted water, and bring to a boil. Cook for 15-20 minutes until tender.

Drain the potatoes and add them to a mixing bowl with butter and warm milk or cream. Mash until smooth and creamy, adjusting consistency as needed.

Let the meatloaf rest for a few minutes before slicing and serve with creamy mashed potatoes.