At this time of year you can often find over-ripe (albeit imported) tomatoes, bought too early by over-enthusiastic retailers, going for a song because they can't yet be sold to customers still hunkered down against the cold weather. I spend happy afternoons cooking these fruits into batches of lovely sauce and freeze them, all the better to enrich mid-season meals like the simple tomato-and-mozzarella pasta bake we enjoyed this evening. This tastes sooo much better than jar-sauces and even sauce made with tinned tomatoes (my cold-weather standby); it is totally moreish and takes very little actual work, honest; just be around to 'poke' it occasionally.
Thrifty Tomato Sauce
Obviously adjust this to the quantity of tomatoes you have, but I thought framing the recipe for one meal's-worth of sauce would probably be the most helpful.
1 onion, chopped
4 cloves garlic, chopped
1 kg tomatoes (overripe, somewhat squishy is fine. Mouldy, however, is NOT )
1 tsp mixed dried herbs
2 tbsp tomato purée
seasoning, to taste
Heat the oil in a large pan, add the onion, garlic and dried herbs and cook until the onion is soft, but not brown. Add the tomatoes and crush lightly (with a potato masher or similar) to pop them and release the juices. Stir in the tomato purée and cook very gently over a low heat for 45 minutes to 1 hour, giving it an occasional spoon-tweak to check it doesn't stick, until the tomatoes are very soft, Purée with a (hand) blender until smooth, then season to taste and cool before freezing.