Heat the oven to 375°F. Lightly grease eight cups of a standard muffin tin.

In a large bowl, combine the ground beef, breadcrumbs, egg, 1/4 cup milk, onion, Worcestershire sauce, garlic powder, salt, pepper, and 2 tablespoons of the ketchup. Mix gently until combined, taking care not to pack the meat mixture too tightly.

Divide the mixture among the eight prepared muffin cups. Shape each portion into a mound, then spread the remaining 2 tablespoons of ketchup over the tops.

Bake for 20 to 25 minutes, until the meatloaves are cooked through. Let them rest in the tin for 5 minutes, then carefully drain off any excess juices.

While the meatloaves bake, put the potatoes in a saucepan and cover them with water. Bring to a boil, then cook until fork-tender, about 15 to 20 minutes. Drain well and return them to the warm pan.

Mash the potatoes with the butter and the remaining 1/4 cup milk until smooth. Spoon or pipe the mashed potatoes onto each baked meatloaf muffin.

Return the topped muffins to the oven for 3 to 5 minutes, until the potato tops are heated through and lightly golden. Serve warm.