Preheat your oven to 375°F (190°C). Grease the muffin tin with non-stick spray or olive oil to prevent sticking.

In a large mixing bowl, combine the ground beef, breadcrumbs, milk, chopped onion, egg, ketchup, Worcestershire sauce, garlic powder, salt, and black pepper. Mix until all ingredients are well combined.

Scoop the meat mixture into the prepared muffin tin, filling each cup about three-quarters full.

Bake the meatloaf muffins in the preheated oven for 20-25 minutes, or until cooked through and the internal temperature reaches 160°F (70°C).

While the muffins are baking, prepare the mashed potatoes. Boil the cubed potatoes in a large pot of salted water for about 15 minutes or until tender. Drain and return them to the pot.

Add the butter and milk to the drained potatoes. Mash using a fork or potato masher until smooth and creamy. Season with salt and pepper to taste.

Once the meatloaf muffins are done baking, remove them from the oven and let them cool for a few minutes. Then, transfer the muffins to a baking sheet.

Use a piping bag or a spoon to pipe or spread the mashed potatoes on top of each mini meatloaf muffin, creating a frosting-like effect.

Serve warm and enjoy your Mini Meatloaf Muffins with Mashed Potato Frosting!