Give the tomatoes a good rinse. I usually de-stem them as well knowing that any juices in the roasting pan will go in the blender too. Roast the tomatoes in the oven (400F) for 20-25 mintues.
Once the tomatoes have been roasting for a bit, saute the roughly chopped 1/2 onion in some oil over medium heat along with the peeled garlic cloves. You can leave the garlic cloves whole as all of this is going in the blender eventually.
Add the roasted tomatoes to the onion-garlic mixture along with: 2 cups cooked beans, 2 cups stock, 1 chipotle in adobo, 1 teaspoon Mexican oregano, 1/2 teaspoon cumin (optional), 1/2 teaspoon salt, and some freshly cracked black pepper. I usually drain and rinse canned beans.
Bring this mixture to a uniform temp and then combine well in a blender. I usually leave it a bit chunky. Be sure to use caution when blending warm ingredients as steam can create upwards pressure on the lid.
Add the bean mixture back to the pan and bring it up to a simmer. Once simmering be sure to give it a final taste for seasoning! I added more salt at this point (so a heaping teaspoon total for this batch) and another generous pinch of Mexican oregano.
Serve immediately with your choice of garnish. I used Mexican Crema, freshly chopped cilantro, and a squeeze of lime.
Store leftovers in an airtight container in the fridge where it will keep for a few days.