The first time I tried to make homemade spaghetti sauce, it was a disaster. I had watched my mother make it, but didn't have a recipe. I was young. My Mom always thickened the sauce with a "little" cornstarch/water mixture. So I tried that. It was still too runny for me, so I added more conrstarch, more constarch, and yuk! It was finally thicker, not runny, but had a very weird pale color and tasted like chalk! I was so embarrassed. Never did that again, without a recipe and to this day, I haven't found a need for cornstarch to thicken tomato sauce - I use tomato paste, so I don't know why my Mom used cornstarch???