On medium-low heat, cook the diced onion in the olive oil in a medium-sized pot just until the onions start to brown a bit on the ends.
Add the tomatoes and their juices to the pot, crushing the tomatoes with the back of a spoon.
Stir in the apple cider vinegar, brown sugar, molasses, chipotle chiles, cinnamon, cloves, celery seeds, and salt, bring to a boil, then turn the heat down to low and then simmer uncovered for an hour, stirring occasionally.
After an hour, puree the mixture, and then continue to cook on low heat until it reaches your desired thickness. Adjust seasonings to taste. Will keep for 2 weeks in the refrigerator.