Preheat your oven to 400°F (200°C).
In a large mixing bowl, combine the ground beef, bread crumbs, Parmesan cheese, milk, egg, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Mix until just combined.
Shape the mixture into meatballs, about 1.5 inches in diameter. Place them on a baking sheet.
Bake the meatballs in the preheated oven for about 20 minutes, or until browned and cooked through.
While the meatballs are baking, heat a large skillet over medium heat and melt the butter.
Add the sliced mushrooms to the skillet and sauté until they are tender, about 5 minutes.
Sprinkle the flour over the mushrooms and stir to combine, cooking for an additional minute.
Gradually whisk in the beef broth, stirring continuously until the sauce thickens.
Reduce the heat to low, then slowly stir in the heavy cream and Worcestershire sauce. Season with salt and pepper to taste.
Once the meatballs are cooked, add them to the skillet with the gravy, gently stirring to coat the meatballs.
Serve hot, garnished with chopped parsley.