Preheat oven to 375°F (190°C).

In a mixing bowl, combine ground beef, breadcrumbs, egg, milk, onion, ketchup, Worcestershire sauce, garlic powder, salt, and pepper. Mix until just combined.

Transfer the mixture to a loaf pan and shape into a loaf.

Bake for 50–60 minutes or until the internal temperature reaches 160°F (71°C).

Meanwhile, boil potatoes in salted water until fork tender (about 15–20 minutes).

Drain potatoes and mash with milk, butter, salt, and pepper.

Let the meatloaf rest for 10 minutes before slicing.

Serve slices of meatloaf with a generous scoop of mashed potatoes.