Saute oil, onion, and garlic in a large, stainless steel stock pot 2-3 minutes.
Add remaining ingredients and bring to a boil.
Reduce heat to low and cook 15-20 minutes.
Blend until smooth with an immersion blender.
Cook for another 20-25 minutes for flavors to meld and sauce to thicken further, stirring often to prevent sticking. Be careful of spatters - you can partially cover the pot if needed.
For water-bath canning:***Prepare jars, lids, and canning equipment while sauce is cooking. Remove sauce from heat and ladle into hot, clean jars one at a time with 1/2-inch headspace.
Remove any air bubbles by running a plastic spatula or knife around the inside of the jars. Wipe rims with a moist towel and attach lids.
Process both pint and 1/2-pint jars for 20 minutes. Remove to a towel-lined surface and let sit undisturbed for 12-24 hours. Check seals, refrigerating any that didn't seal, label and store for year to year and a half.
Notes
*For a spicier sauce, you can use the whole can, but it will be very spicy. For a less spicy sauce, use 2-3 chipotle peppers in adobo - you'll still get the good, smokey flavor with just a hint of spice.**Or use an equal amount of organic canned tomato sauce.***TO FREEZE: Let sauce cool a bit and then ladle into freezer-safe storage containers, leaving 1-2 inches headspace for expansion. Label and use within a year.-High Altitude Adjustment: If processing at an altitude of higher than 1000 feet above sea level you'll need to adjust the processing time according to this chart. -If you have any jars that didn't seal (which is rare!), store them in the fridge and use first.