Start by giving the tomatoes a good rinse. I usually de-stem them as well knowing that any juices leftover in the roasting pan will go in the pot. Roast the tomatoes in the oven (400F) for 20-25 minutes or until you need them.
Roughly chop the onion and peel 4 garlic cloves. Cook the onion and garlic in a glug of oil over medium heat. I used a medium-sized soup pot. I left the garlic cloves whole for this batch, knowing that all of this will be blended eventually.
When the onion is starting to brown you can add the spices: 2 teaspoons Mexican oregano, 1/2 teaspoon cumin (optional), 1 teaspoon salt, freshly cracked black pepper. Stir well to give the spices some direct contact with the heat.
Add the remaining ingredients: 2 cans pinto beans (drained and rinsed), the roasted tomatoes, 1-2 chipotles in adobo (or just some adobo sauce!), and 4 cups of stock. Bring this mixture up to a simmer.
Add the mixture to a blender and combine well. Be sure to use caution when blending warm liquids. It can help to NOT fill the blender all the way, ie blend in batches.
Add the soup back to the pan and simmer over medium-low heat as you do the final taste testing. I added another generous pinch of salt to this batch, but keep in mind the exact salt level will depend on which stock you're using. I also added another pinch of Mexican oregano and more adobo sauce. Note: if it ever seems like the broth is on top and the blended beans are sinking to the bottom, this is a sure sign that you need to blend the soup more thoroughly.
Once you're happy with the final taste test you can serve it up! Alternatively, if you want to thicken up the soup you can just let it simmer a bit longer, uncovered.
Feel free to garnish with your choice of fixings. For this batch I topped with Crema, freshly chopped cilantro, a few drops of hot sauce, and a final squeeze of lime. Yum :)