Cover the tomatoes, onion, and garlic with water.
Bring to a boil. Cook for 3 minutes, or until tomatoes are soft.
Let cool slightly.
To a blender, add the tomatoes, chipotle, onion, garlic, and salt.
Blend until smooth.
To make the salsa last longer and to make it thicker, cook it.
In a large pan, heat up the oil.
Stand back and slowly add some of the tomato mixture.
Immediately add a little more of the tomato mixture.
Then add the remainder of the mixture.
Bring to a simmer and reduce heat.
Cook on low heat for 15 minutes.
The sauce will thicken up.
Let cool and store.