Good tomatillo selection is hard to come by off-season where I live, so I think using a good, relatively preservative free tomatillo salsa is a great substitute. Just make sure the salsa verde is based on tomatillos and not all jalapenos.
I tend to order my dried beans in bulk, because I prefer good heirloom beans and there is flat rate shipping. Because of this, my beans can get old, so I prefer to soak overnight. If your beans might be older, I definitely recommend it.
The day of cooking, bring the beans to a boil covered by 2 inches of water. Add the onion, oil and garlic. Make sure everything is still covered by 2 inches of water.
Bring beans to a rolling boil for 5 minutes, and then cover and reduce heat to very gently simmer. Check every hour or 2 to make sure the beans are still covered by 2 inches of water.
When the beans are mostly tender, add 1/2 teaspoon of kosher sea salt.
Heat the oil in a large Dutch oven or heavy stock pot over medium high heat. Brown the chicken in whole pieces on both sides, and then remove and chop them into bite sized pieces. Let rest in bowl.
Add the chopped onions with a pinch of salt and the cider vinegar to deglaze the pan. Scrape up all of the yummy stuck bits and then let the onions cook, stirring occasionally, until they are starting to caramelize.
Add the minced garlic and let cook, stirring, another 2-3 minutes.
Add the potatoes with the Mexican oregano and the cumin and another pinch of salt. Toss to evenly coat the potatoes. Let cook without stirring over medium heat for 5-10 minutes until the potatoes have a golden crust on the bottom.
Add the stock and salsa with the canned tomatillos (if using--if not, add more salsa). Stir and make sure none of the potatoes are sticking.
Add the chicken back in, along with any accumulated juices. Add the cooked beans to the pot along with the bean stock. Simmer for 25 mins (you can cover the pot if the soup seems dry, or leave uncovered if it is soupy--your call!).
Add asparagus pieces and simmer an additional 5 minutes, until asparagus is bright green and tender.
Taste the soup for salt, honey, cider vinegar or more salsa. Mine needed a pinch of salt, about 1 tablespoon each of honey and cider vinegar, and then I served each bowl dolloped with another spoonful of salsa.
This soup actually froze really well--I made double the recipe above and it saved us while we were moving and getting really tired of eating out. The asparagus got a little mushy, but not enough that it bothered any of us for a weekday, casual meal.
If you use canned tomatillos that are super firm you might want to quarter them before adding to the pot. My mom's were not.