Wash the tomatoes and place them in a large pot with the chiles, garlic, and onions. Cover them with water and bring to a boil over medium-high heat. Reduce the heat and simmer for 15 – 20 minutes until the tomatoes are a bit mushy and the chiles are soft.
While the vegetables simmer, mix together the salt and pepper in a small ramekin and set aside.
Using a slotted spoon or a spider strainer, transfer the vegetables in batches to a blender, add some of the salt and pepper and puree until smooth.
Once all the veggies have been processed, heat the oil in a large stock pot over medium heat. When the oil is hot, pour in the salsa, bring it to a simmer, and cook it for 10-15 minutes until the sauce begins to thicken and the color deepens.
Pour into hot, sterilized pint jars, top with lids, and process in a boiling water bath for 20 minutes.
Remove from the canner, cool, and check seals. Can be stored in a cool dry place for up to a year.