In a large casserole dish heat some oil and gently fry the meatballs until golden brown all over. Transfer them to a plate.
Meanwhile chop the onion, garlic, celery, carrot and bell pepper, then gently fry these over low heat (after you removed the meatballs from the pan).
When the vegetables are soft, add the tomato purée, stir for a few seconds, then add the tinned tomatoes. Season with salt.
Bring to the boil then simmer for about 15 minutes. Stir in the herbs, then using a hand-held blender whiz until you get a thick sauce. Taste it. If it’s not sweet enough, add a small spoonful of brown sugar.
Return the meatballs, put the lid on and cook for a further 10 minutes or so (you can add some grated mozzarella for the last 5 minutes if you like it gooey). Season with plenty of freshly ground pepper.
Serve and scatter some Parmesan and/or chopped herbs on top.