If you want to thicken spaghetti sauce, be sure to use a full can of tomato sauce or tomato paste.
Stir in the desired amount until it is the consistency desired. Allow the mixture to cook for about 10 minutes before adding any other ingredients. This allows the thickening to take effect.
When you are making a large amount of spaghetti sauce, white sugar can be added for sweetness.
This will also allow any other ingredients in the sauce to blend better. The amount needed is 2 tablespoons per every 6-ounce can of tomato paste or 3 tablespoons per 28-ounce can of whole tomatoes.
If you want to thicken spaghetti sauce, mix 1 tablespoon of cornstarch with 2 tablespoons of cool water. Add this mixture slowly into the sauce while it is still cooking and stir constantly. If your sauce becomes too thick, add more water or milk, as needed.
So this is how to thicken the spaghetti sauce!