Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine the ground beef, bread crumbs, Parmesan cheese, parsley, egg, minced garlic, onion powder, salt, and pepper. Mix until just combined.
Shape the mixture into 1.5-inch meatballs and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for 20-25 minutes, or until browned and cooked through.
While the meatballs are baking, heat olive oil in a skillet over medium heat. Add diced onions and sauté until translucent, about 5 minutes.
Sprinkle the flour over the onions and stir to combine. Cook for 1 minute.
Gradually whisk in the beef broth and bring the mixture to a simmer. Allow it to thicken slightly.
Stir in the heavy cream and Worcestershire sauce. Continue stirring until the gravy is smooth and heated through. Season with salt and pepper to taste.
Once the meatballs are done baking, add them to the skillet with the gravy. Stir gently to coat the meatballs with the sauce.
Let everything simmer together for an additional 5 minutes for the flavors to meld.
Serve the smothered meatballs hot, garnished with chopped parsley if desired.