Put the peeled onion and the celery into a food processor and blitz to a mush. Or you can chop as finely as humanly possible by hand. Reserve two tablespoons for the meatball mixture.
Warm the garlic oil in a large heavy-based saucepan or casserole, add the onion and celery mixture, along with the thyme, and cook at a moderate to low heat, stirring every now and again, for about ten minutes. Add the cans of tomato, filling up each empty can with water to add to the pan. Season with the sugar, salt and pepper, stir and let it come to a bubble, then turn the heat down to simmer gently while you get on with the meatballs.
Put all the ingredients for the meatballs, including the reserved chopped onion and celery, and salt according to preference, into a large bowl and mix together, gently, with your hands. Don't over-mix, as that will make the meatballs dense-textured and heavy.
When all the meatball ingredients are not too officiously amalgamated, start rolling. The easiest way is to pinch out an amount about the size of a generously heaped teaspoon and roll into a ball between the palms of your hands. Put the meatballs on a baking tray, lined with baking parchment or greaseproof paper, as you go. You should get about 50 little meatballs.
Drop these gently into the simmering sauce; I try to let these fall in concentric circles working round the pan from the outside edge inwards, in the vaguest of fashions. Let the meatballs simmer for 30 minutes, until cooked through. Serve with rice or pasta, or however you so please.
Recipe from Nigella: Kitchen by Nigella Lawson (published by Chatto & Windus).