I just went a searched for where I posted this elsewhere on t'interweb - I knew it was out the somewhere for me to copy and paste
I used to volunteer on a rare breeds farm in the south of France and, since I knew nowt about farming, decided to do lots of the cooking whilst I was there as it seemed the most helpful thing to do. I also, eventually, worked out the difference between weeds and not weeds, and so did quite a bit in the veg garden. Although in the 4 summers that I spent there we never quite reached our (self-imposed) 'target' of growing a hundred tomato plants, we did get to well over 80 once. So one fairly regular job was to go and harvest ripe toms by the wheelbarrow-load!
I used to give them a quick rinse, chop them very roughly - halved or quartered - and chuck them in the jam pan with a generous sprinkling of salt. Occasionally I'd get sophisticated and chuck in garlic/herbs etc - rosemary and bay both worked quite well. Slowly heat, so that the juice starts to flow and it doesn't burn, and once it's looking like there's plenty of liquid turn it up a bit and ignore for at least an hour. Take off the heat, and run it through a mouli to puree it and get rid of the skin. Chuck it back in the jam pan, put it on a low heat (back of the rayburn worked well, when it was on) and let it simmer for multiple hours, stirring occasionally, until it's fairly thick - thicker than passata, but not puree!
I stored it in old wine bottles - thoroughly washed out, and rinsed in boiling water but never properly sterilised tbh. Fill up to just above the level of the start of the neck (using a funnel) with the hot tomato stuff, then pour in an oil 'bung' a couple or three centimtres deep of decent quality olive/sunflower oil. Cover the tops (or loosely cork) and store in a cool dark place. Kept right through the winter, and I never found a bad bottle.
It did mean a LOT of pasta and tomato sauce got scoffed in the early spring when there wasn't much else from the garden to eat!