In case you haven't tried it
www.thekitchn.com/marcella-hazans-amazing-4ingre-144538
It's basically 1 tin of tomatoes cooked on a medium heat with half an onion and 5 tablespoons of butter for 45 minutes or so. A bit of stirring now and then.
It's so so good. Really rich and delicious. We didn't have anything else with it, just parmesan and pasta. Yum.