To begin, wash the tomatoes and remove the stems. Then, score the bottom with an X.
Fill a large bowl with ice water and set aside.
Bring a large pot of water to a boil. Lower the tomatoes into the water and allow them to boil until the skins begin to peel back slightly. This takes about a minute.
Then, remove the tomatoes from the water and place them in the ice bath to stop the cooking process. Allow the tomatoes to soak in the ice bath until the skins begin to shrivel. Then, remove them from the ice water and peel the skins off the tomatoes.
Next, heat a large skillet over medium heat. Add the peeled and halved garlic. Add the peeled tomatoes. Cover with a lid and allow to cook for at least an hour, mixing occasionally.
Remove the garlic.
Pass the tomato mixture through a fine mesh sieve or food mill to remove the seeds.
Return the sauce to the pan, adjust the heat to low, season with salt and add basil leaves.
At this point, the tomato sauce is ready to use. If you plan to freeze it, allow it to come to room temperature, and then transfer it to freezer safe containers.
