Preheat your oven to 190°C/375°F/gas 5 and lightly oil a roasting tin. Fill with halved tomatoes, cut side up and tightly packed, then sprinkle them with salt, pepper and a little sugar. Dress them with olive oil and roast for 20 minutes.
Dice 225 g/ 8 oz onion, 4 garlic cloves and 1 hot red chilli and scatter over the tomatoes. Dress with more oil and return to the oven for 20–30 minutes, when the tomatoes will have shrunk and the onions browned. Check at regular intervals during this second roasting period that they are not burning. If you allow them to burn you will make the sauce bitter and unpleasant.
Remove from the oven and, when cool, purée and sieve before packing in jars and filming the surface with oil to store.
You can ring all kinds of changes at the puréeing stage. Try adding anchovies or stoned, black olives or basil.