I'm very particular about the tomatoes I use in this sauce. Look for canned crushed tomatoes, some cans you will come across will say "with added puree" - this is also fine. I avoid diced tomatoes, pass on pureed, and skip whole tomatoes as well. Avoid the crushed tomatoes with added herbs, seasonings, etc. You want pure crushed tomatoes if possible. I also look for organic crushed tomatoes which can be tricky, I often come across the Muir Glen brand, it has added basil in it - that one is actually fine. The San Marzano crushed tomatoes are great as well. Any leftover sauce keeps well in the refrigerator for three or four days.