For the meatballs: Just put everything in a large bowl and then, using your hands, mix to combine before shaping into small balls.Place the meatballs on baking sheets or plates that you have lined with clingfilm, and put each in the fridge as you finish them. For the tomato sauce: Put the onion, garlic and oregano into the processor and blitz to a pulp.Heat the butter and oil in a deep, wide pan, then scrape the onion-garlic mix into it and cook over low to medium heat for about 10 minutes. Don’t let the mixture catch, just let it become soft.Add the tomato passata and then half-fill the empty bottle with cold water (approx. 300-350ml / 1 1/4 cups water). Add this to the pan with the pinch of sugar and some salt and pepper, and cook for about 10 minutes. The tomato sauce will appear thin at this stage, but don’t worry as it will thicken a little later.Stir in the milk, and then drop the meatballs in one by one. Don’t stir the pan until the meatballs have turned from pink to brown as you don’t want to break them up.Cook everything for about 20 minutes, with the lid only partially covering it. At the end of cooking time, check the seasoning, as you may want more salt and a grind or two more of pepper.