Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

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

Shape the mixture into uniform meatballs about 1.5 inches wide and place them on the baking sheet.

Bake the meatballs for about 20 minutes or until browned and register an internal temperature of 160°F (70°C).

While the meatballs bake, add peeled and chopped potatoes to a saucepan and cover with cold water. Bring to a boil over medium-high heat and cook until fork-tender, about 15 to 20 minutes.

Drain the potatoes, return them to the saucepan and add garlic, butter, and milk. Mash until smooth and creamy, stirring in parsley, salt, and pepper.

For the gravy, heat a frying pan and add flour, cooking for about a minute. Gradually whisk in beef broth, add soy sauce and mustard, and let simmer until thickened, about 5 minutes.

Carefully coat the baked meatballs in the thickened gravy.

Serve by placing mashed potatoes on plates, topping with meatballs, and spooning additional gravy over, garnished with fresh parsley.