Preheat oven to 425 degrees F.
Place all of the meatball ingredients into a large mixing bowl and mix thoroughly with your hands.
Line a large baking tray with non-stick paper and shape your meatballs with your hands.
You should get approx. 20 golf ball sized meatballs. Bake for 30 minutes.
While the meatballs cook, place the butter into a large, deep sided pan.
Thinly slice your onions and cook them over med-high heat until they are caramelized.
Add the beef stock and the garlic, salt and pepper and simmer until the sauce is reduced and thickened.
Nestle the meatballs into the sauce and top with the extra mozzarella cheese.
You can either broil the pan until the cheese melts or place a lid on it on the stovetop and cook on low until the cheese melts.
Serve garnished with chopped parsley.
Store in the refrigerator for up to 5 days.