Passata is made from skinless and de-seeded strained tomatoes, and it's wonderfully smooth and rich. You can usually find it with canned goods in the grocery store, next to canned tomatoes and tomato paste. If you can't find passata, you can use canned crushed tomatoes. They won't have been seeded, but other than that they are essentially the same thing. They will require a slightly longer cooking time to break down into a sauce, whereas passata already has a thick sauce consistency.