Peel and rinse tomatillos. Arrange on a foil-lined sheet. Add poblanos and serranos. Roughly chop the onion and add to the tray. Slice the top off of the garlic bulb and add the bulb to the tray.
Drizzle the garlic and vegetables with one tablespoon olive oil. Broil the vegetables on high until charred.
While the vegetables are in the oven, salt, and pepper the cubed pork. Heat the remaining oil in a cast-iron skillet. Sear the meat, working in batches. Add the seared meat to a crockpot, including the pan juices.
Peel the skin off of the charred peppers and garlic once they're cool enough to handle.
Add the pan ingredients, cilantro, cumin, and oregano to a blender. Top chicken broth. Depending on the size of your blender, you might have to do this in batches. Pulse the vegetables until roughly chopped.
Pour the mixture over the meat in the crockpot. Cover the crockpot and cook for four to six hours. Serve in a bowl, with a dollop of sour cream and a side of tortilla chips.