The good thing is that tomatoes are not only a nutrient dense vegetable, but they are also rich in lycopene, a powerful antioxidant responsible of their red color, which is especially abundant in cooked tomatoes products.
The sauce can be made with whole tomatoes or just the flesh. I prefer the latter, but it will take some time to prepare the tomatoes. If you don't have that extra time, start directly in step 3.
You'll notice that there are no amounts in the recipe, everything is to taste.
1) Start by peeling the tomatoes. The easiest way to do this is to cut and X in the top or bottom of the tomatoes. Blanch them for 25 seconds and very quickly put them into an ice water bath. Now it will be very easy to peel the tomatoes.
2) Remove the seeds from the tomatoes. You can either cut them in four pieces and remove the seeds one by one or you can make a cut in one side of the tomato, turn the knife and cut around the center pulp and seeds removing the flesh in one long strip. Then cut the strips into smaller pieces.
3) After that you'll just need to sauté onions in olive oil for approximately 5 to 8 minutes. Remember to salt the onions when you are sautéing them because this will release all the water from the onions and they will cook in that liquid. Add chopped garlic and sauté for 30 seconds and add the tomatoes. As soon as you ad the tomatoes add salt, pepper, oregano (dried or fresh as you prefer), bay leaves, sometimes I add some red wine and anything you want to condiment the sauce. Add some sugar (a tablespoon) to cut the acidity.
4) The sauce should be cooked in a covered pot over low heat for one or two hours. Don't use aluminum cookware since the high acid content of the tomatoes may interact with the metal. If you have a slow cooker you can cook the sauce there (but you need to sauté the onions with the garlic and tomatoes before) in the slow setting for 4 hours or more. The longer you cook the sauce, the sweeter it will be.
5) Puree everything in a food processor, let it cool, fill glass containers and put them in the freezer. It is a good idea to use different sizes of jars so you have tomato sauce for different recipes. Once you thaw them it is not a good idea to re-freeze.
I use this sauce in lots of different dishes as pasta, pizza, rice, polenta and quinoa, and depending on the use sometimes I add fresh basil, black olives, more onion, meat, etc. It is a nice way to introduce more vegetables to the snacks and lunches that we bring to school.