Put everything into a large slow-cooker (except peppers if adding) and stir well.
If you want to add the peppers for a kick, I love to toss them onto the BBQ or grill over medium heat for about 2-4 minutes a side to char the outsides. Remove from heat, cut off the ends, slice the pepper in half and remove the seeds. Loosely chop the peppers and add to the slow-cooker.
Place the lid on and cook on high for 1 hour, then reduce the heat to low and let cooker for 6-7 hours.
Once the sauce is done, you may notice some excess liquid sitting on the top. A little is ok, but the more you remove the thicker the BBQ sauce you will have. This typically varies from how juicy the tomatoes were. I use a large ladle and push down along the inside of the pot, the liquid flows in and I discard that.
After most of the liquid is removed scoop it into a blender or place an immersion blender into the slow-cooker and process till smooth, based on how you like your sauce.
You can store it in sealed jars in the fridge for 3 weeks. If you wish to can them for storing in the pantry for 1 year use the canning method in the recipe notes below.