【How-to】How can i thicken tomato sauce without tomato paste

First, add a very small amount of starch, like cornstarch or a roux. Next, add a little bit of tomato paste to thicken things up more and improve the flavor. Finally, stir your sauce and simmer it for at least 10 minutes. In most cases, this will give you a very thick spaghetti sauce that will impress your guests.