Preheat oven to 300 º
Start by placing the onion quarters in the bottom of a dutch oven or large pot that will fit in oven
Sprinkle the pork with salt and pepper, then place of top of the onions.
Pour the chipotle peppers over the top, and crack open the cans of coke and pour them over all.
Add brown sugar to the liquid and stir.
Cover the pot, put in the oven, and cook for at least 6 hours., flipping the roast 2 or 3 times during the cooking process. When it is done, the pork will be dark and weird and wonderful.
It will also be fork-tender. That is when you know it is done.
Remove the meat from the pot and shred completely. Then return the meat to the pot and keep in the juice until you are ready to eat it.