Add the onion, carrots, and celery and to a food processor and chop it into small pieces.
Heat 2 tablespoons of the olive oil in a large saucepan on medium heat and saute the onion, celery, and carrots until they are soft and no liquid is being released from them.
In the middle of the softened vegetables, form a well, add the remaining olive oil, followed by the garlic. Allow the garlic to brown slightly (being careful not to let it burn).
Mix in the tomatoes and herbs.
Add seasoning, bring to a boil, lower the heat, and simmer for 30 minutes.
If you like a thinner sauce you can add it to the food processor and puree into your desired consistency or if you like a thicker sauce, skip this step.
Baking soda neutralizes acidity. To save bitter sauce, add an eighth of a teaspoon of baking soda at a time tasting in between until the acidity dissipates. Alternatively, try adding sugar 1/2 tablespoon at a time (tasting in between) will cut the acid.
This tomato sauce will thicken as it cooks. If it becomes too thick, you can add a little water to loosen it up.
If you don’t have fresh herbs on hand, they can be substituted for dried. Dried parsley has next to no flavor so I suggest using oregano in its place.
Using Fresh Tomatoes
To use fresh tomatoes you will need 4 lbs of tomatoes, cut into quarters, and coat with olive oil and salt and pepper, and roast at 400°F for 30-35 minutes (keep an eye on them if you don't want them browned) then I puree the mixture until smooth. This is a great way to keep them from becoming too watery (although tomato paste may need to be added to thicken in the sauce). Then use as you would canned tomatoes.