In the same pan where we seared the meatballs add more olive oil if needed and cook the onion on low heat until soft, translucent and sweet in smell.
Add the garlic and bayleaf and cook for a minute.
Add the tomato paste and cook for another minute.
Add the chopped tomatoes and increase the heat to medium. Mix until it's hot and letting out a lot of steam.
Add enough vegetable stock to cover and let it cook until the tomato starts to disintegrate. When it starts to thicken add the meatballs, cover and let them finish to cook in the sauce.