Heat olive oil in a large pot over medium heat. Saute onions until they are translucent and starting to turn golden brown. Add minced garlic and cook another 60 seconds.
Turn heat down to medium-low and add tomatoes to the onions and garlic, giving it a good stir. (Tip: if your pot isn't going to be large enough, chop the tomatoes into even smaller pieces and your tomatoes will fit much better!)
Giving the occasional stir, allow tomatoes to simmer and cook down for two hours.
Take an immersion blender to the sauce and puree it to your desired consistency. Add spices.
Continue to allow sauce to simmer for another 2-3 hours.
At this point sauce should be greatly reduced, thick, rich, and delicious!
Allow to cool completely before portioning sauce into freezer-safe bags or containers (we did two-cup bags). For easier storage, freeze the bags flat.
Sauce can remain in the freezer about 6 months, or longer if a deep freezer.