Mix the ground beef, breadcrumbs, egg, garlic powder, onion powder, and Worcestershire sauce gently in a bowl. Form into golf-ball-sized meatballs.
Sear the meatballs in olive oil over medium-high heat until browned, then remove from the pan.
Sauté the sliced onions and mushrooms in the remaining beef fat over medium heat until soft.
Sprinkle flour over the vegetables, stir for one minute, then slowly pour in the beef broth.
Simmer the meatballs in the gravy for 15 minutes until fully cooked and the gravy has thickened.
Boil the cubed potatoes in salted water until tender, drain, and return to the hot pot to evaporate excess moisture.
Mash the potatoes by hand, folding in the heavy cream, butter, minced garlic, salt, and fresh parsley.
