Full-bodied, rich and thick are words that describe a quality spaghetti sauce. Simply heating tomatoes for a short period of time with a little Italian seasoning yields a marinara sauce with little substance. Here's how to create a thicker, richer, better sauce.
Cook the Sauce Longer
Sauté garlic and onions for a few minutes in olive oil, then add crushed tomatoes with some herbs and spices. The process only takes 10 minutes or so to heat, but simmer it for at least 45 minutes to thicken.
Just Add Carrots
Add puréed carrots to thicken and sweeten the sauce. Cook the onions, garlic and tomatoes as your recipe requires. In a separate pan, cook one large carrot, chopped, in olive oil and enough vegetable or chicken broth to cover it. Simmer until the carrot is soft, and then purée it in a food processor or blender. Add the carrot to the tomato sauce along with any seasonings. Simmer for 10 to 15 minutes, or until desired thickness is achieved.
Keep It Starchy
As it cooks, pasta releases starch which you can use also to thicken spaghetti sauce. The key is,
Don't use flour or cornstarch. Flour adds a pasty consistency and taste that is inappropriate for a good, tomato-based sauce. Cornstarch also adds a clashing flavor to the sauce and doesn't thicken well due to the acidity of the tomatoes. Save flour or cornstarch for gravies, Asian dishes and desserts.