Preheat oven to 400℉
Wash and cut tomatoes in half and place on a foil lined sheet pan. Roast the tomatoes until the skins begin to lift off the tomatoes and blacken, approximately 15 minutes per pan. This will make removing the skins incredibly easy.
Dice yellow onion and sauté in olive oil in the stock pot over medium heat until tender and translucent.
Once the tomatoes are roasted, remove from the oven and carefully pull the skins off with a tongs. Scoop tomatoes into a food mill over the stockpot and process through to remove the seeds. Continue with roasting the tomatoes until entire batch is roasted and processed through the food mill into the stockpot.
Using the immersion blender, blend the onions in the tomato juice until smooth.
Add all the remaining ingredients and spices to the stockpot and simmer for 2-3 hours. The sauce should be reduced and thickened. It can simmer longer if needed, which will yield a thicker BBQ sauce.
Fill water bath canner with water and bring to boil.
Wash all jars, lids, and rings in hot soapy water and allow to air dry.
Fill each jar, leaving 1/2-inch headspace. Remove any air with the bubble popper.
Wipe rim of jar with a clean paper towel, place lid on top and secure with the band, fingertip tight.
Place jars into the water bath making sure all the jars are covered by the water by at least 1 inch.
Place the cover on the water bath and process for 20 minutes.
After the processing time, turn off the stove, remove the cover and allow the jars to rest in the water for 5 minutes.
Using the jar lifter, careful not to tip the jars, remove them and place onto a towel lined wooden cutting board. The jars will seal rather quickly, but let the jars sit undisturbed for 24 hours. Label and date the jars.
Store in a cool, dry area for up to 2 years.