Fill a large pot with water and bring to a boil. Meanwhile, prepare an ice bath. Core out the stems from the tomatoes and slice a shallow "X" in the bottom of each tomato.
Blanch the tomatoes in boiling water for 30-60 seconds, then transfer to ice bath. Remove the skin from the tomatoes.
Chop the tomatoes into small chunks and set aside.
In a large pot heat olive oil. Add chopped onion and sauté over low heat until golden, about 7-8 minutes. Add crushed garlic and sauté for 2 minutes more.
Add chopped tomatoes to the pot, season with salt, oregano, and basil. Bring the mixture to a boil, reduce the heat and simmer for 60-90 minutes, until it reaches the the desired consistency (until almost all the liquid has evaporated, and the tomatoes are reduced to a thick, jam-like consistency). Stir frequently.
At the end add the vinegar, stir and turn the heat off.
If you prefer smooth tomato sauce, purée the sauce using a hand blender. Transfer to a jar.