I use one of those really large tins (2.5kg size) of tomatoes in this sauce. I purchase mine from my local Italian deli. If you cannot locate this size tin, substitute 3 x 800ml tins of tomatoes instead. I know it looks like a large amount of olive oil, but trust me. You are not cooking a single meal (unless you have an extremely hungry family) so this amount of oil is necessary to saute all of the vegetables.