In a food processor, add in the onion, garlic cloves, parmesan cheese, parsley and bread and turn it on until everything has been shredded into small bits. If you don't have a food processor, check notes for substitution.
In a large bowl, add the beef mince, salt, pepper, egg and the bread mixture from the food processor and use your hands to mix everything together until combined.
Shape the meat mixture into medium sized balls, I use an ice cream scooper to make them all the same size but using your hands are absolutely fine. Make sure to roll them into smooth balls.
In a medium to large fry pan, on medium heat, heat up the olive oil.
Cook the meatballs in batches, if your pan is big enough, you may be able to do it in two batches. Cook until the meatballs are seared brown on most sides, don't worry if it's not cooked all the way through, they'll cook through in the sauce, just wait to eat them at the end. Don't worry about any stuck bits or colour on the pan, they add flavour to the sauce. Once cooked on the outside, remove from the pan. Note 7
Turn the heat down to medium low, there should be some fat left in the pan from cooking the meatballs, if it's a bit dry, add some olive oil. Add the diced onion to the pan and cook until the onions are soft and start developing colour, 3-5 minutes. Add in the garlic and cook for 1 minute.
Add in the bottle of tomato passata to the pan; pour the beef stock into the bottle of passata and shake it until the leftover tomato passata has mixed with the beef stock and pour it into the pan. Stir to combine.
Add in the Italian herbs, bay leaves, salt, pepper, chilli powder, sugar, tomato paste and vegemite to the sauce and stir to combine. Add the meatballs back into the pan.
Leave the sauce to simmer until it thickens to your liking, I usually do it for around 15 minutes.
Once you have your desired consistency, add in the thickened cream. If it makes your sauce too runny, leave it to simmer a few minutes longer to get it back to your desired consistency.
This would be the time to test how the sauce tastes and make any adjustments. Maybe you'd like it sweeter or saltier or creamier.
Serve with your favourite pasta or in a sub with cheese.