Preheat the oven to 400 degrees F and line a large baking sheet with parchment paper or foil.

In a large mixing bowl, combine the ground beef, breadcrumbs, milk, onion, garlic, egg, Worcestershire sauce, salt, pepper, dried parsley, onion powder, and garlic powder. Mix until just combined. Do not overmix.

Shape the mixture into 1.5-inch meatballs and place on the prepared baking sheet. Bake for about 20 minutes until browned and cooked through to an internal temperature of 165 degrees F.

While the meatballs bake, bring a large pot of salted water to a boil. Add the chopped potatoes and cook for 15 to 20 minutes until fork-tender. Drain and return to the pot. Add the minced garlic, butter, and milk. Mash until smooth and creamy. Stir in fresh parsley off the heat and season with salt to taste.

While the potatoes cook, make the gravy. In a medium skillet over medium heat, add a small knob of butter or drizzle of oil, then whisk in the flour and cook for about 1 minute, stirring constantly, until it smells slightly nutty. Slowly whisk in the beef broth a little at a time to avoid lumps. Stir in the soy sauce and Dijon mustard. Cook, stirring frequently, until the gravy thickens, about 4 to 5 minutes.

Add the baked meatballs to the gravy in the skillet. Stir gently to coat and simmer on low heat for 3 to 5 minutes.

Spoon the mashed potatoes onto plates or into bowls and top generously with Salisbury Steak Meatballs and gravy. Garnish with fresh parsley if desired.