Warm a pan and add the olive oil. As soon as the oil is hot, check that the stove is on low flame and add the garlic. Sauté for about 5 seconds, stirring so that the garlic does not brown.
Add the basil and stir. Add the tomatoes, stir. Bring the stove heat to high for just 2 minutes, stirring the tomatoes and garlic well.
Reduce the flame to low and allow the tomatoes to cook in their juices, stirring frequently and checking that the sauce does not catch at the bottom of the pan.
In about an hour, the sauce will thicken and reduce to about half its original quantity. if you are making a lesser quantity, eg 2 cups of tomatoes to make 1 cup of sauce, the sauce would take lesser time, about 45 minutes. Remember to keep the sauce on low heat and to stir it frequently.
Season with a pinch of salt and the pepper, stir and transfer to a cool bowl so that the sauce does not continue to cook.
Use immediately or freeze after it cools completely, making sure you have not allowed any moisture to enter the sauce. Bring to room temperature and then warm it up again before using.