Make the mashed potatoes: Boil peeled and chopped potatoes in salted water until fork-tender, about 15–20 minutes. Drain and mash with butter, milk, salt, and pepper. Keep warm.

1. Make the meatballs: In a bowl, combine ground beef, breadcrumbs, egg, milk, Worcestershire sauce, onion powder, garlic powder, salt, pepper, and parsley. Mix and form into 1.5-inch meatballs.
2. In a large skillet, heat a bit of oil over medium heat and brown the meatballs on all sides. They don’t need to cook through fully. Remove and set aside.
3. Make the gravy: In the same skillet, melt butter and sauté onions for 8–10 minutes until golden. Add garlic and cook for 1 minute.
4. Sprinkle in flour and cook for 1–2 minutes, stirring constantly.
5. Gradually whisk in beef broth, Worcestershire sauce, and Dijon mustard. Simmer until thickened, about 3–5 minutes.
6. Return meatballs to the skillet, cover, and simmer for 10–12 minutes, or until meatballs are cooked through.
7. Serve meatballs and gravy over mashed potatoes. Garnish with chopped parsley if desired.