Preheat your oven to 400°F (200°C).
In a mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, egg, minced garlic, salt, and black pepper. Mix until just combined.
Shape the meat mixture into 1-inch meatballs and place them on a baking sheet.
Bake the meatballs in the preheated oven for about 15 minutes or until they are cooked through (internal temperature of 160°F).
Meanwhile, in a skillet over medium heat, add olive oil and sauté the chopped onion until translucent, about 5 minutes. Add the minced garlic and cook for another minute.
Pour in the beef broth and Worcestershire sauce, and add thyme. Stir well.
Bring the mixture to a simmer and let it cook for 5 minutes.
If you prefer a thicker gravy, mix cornstarch with a tablespoon of water to create a slurry, then add it to the skillet, stirring until the gravy thickens. Season with salt and pepper to taste.
Once the meatballs are done baking, transfer them to the skillet with the gravy and gently coat them. Let them simmer together for another 5 minutes.
Serve hot over rice, mashed potatoes, or pasta, garnished with additional parsley if desired.