Preheat your oven to 350°F (175°C).

In a large mixing bowl, combine the ground beef, breadcrumbs, milk, onion, Parmesan cheese, egg, garlic powder, salt, and pepper. Mix until just combined.

Form the meat mixture into a loaf shape and place it in a greased baking dish or on a lined baking sheet.

Bake in the preheated oven for 45 minutes.

While the meatloaf is cooking, peel and chop your potatoes into even pieces.

Boil the potatoes in salted water until tender, about 15 minutes. Drain and let them sit for a minute or two.

In a mixing bowl, mash the potatoes with butter, sour cream, and additional salt to taste.

Once the meatloaf has reached an internal temperature of 160°F (70°C) and is browned on top, remove it from the oven and let it rest for 10 minutes before slicing.

Serve your slices of meatloaf on a mound of mashed potatoes, topping with a sprinkle of additional cheese if desired.