Method
Bring a large pot of water to a boil.
With a sharp paring knife, remove the core from each tomato and score an X on the bottom of each.
Place the tomatoes in the boiling water for about 1 minute. Remove the tomatoes and let them cool.
Peel the tomatoes, cut them into wedges, and remove the seeds. Strain the seeds and save the juice.

Dice half of the tomatoes. Puree the remaining tomatoes in a blender.
In a pot, sauté the onion and garlic in olive oil.
Add the diced tomatoes, pureed tomatoes, oregano, salt, and pepper. Cover and cook over low heat for about 30 minutes, stirring occasionally. For a thicker sauce, cook uncovered for a few more minutes.

Add the basil during the last minute of cooking.
Taste and adjust the salt if needed.
Do not add sugar.