Wash the tomatoes and remove any stems.
~30 garden ripe plum tomatoes
Heat the oil in a larger sauce pan and sauté the onion and garlic.
2 onions chopped, 1 tablespoon olive oil, 9 cloves of garlic
While the onion is cooking, puree the tomatoes, basil leaves, and garlic cloves in the blender. You may have to do two batches depending on how large your blender is. The puree will look pink. That's ok, it will darken while cooking.
~60 basil leaves, Kosher salt, 1-2 teaspoon of garlic powder, 1-2 teaspoon italian seasoning
Add the puree to the pot with the onions and bring to a boil while stirring. Once boiled, lower to a simmer and cook all day. I'd say at least 4-5 hours.
Stir occasionally, and after a few hours taste test and add the dry spices.