Boil about 2 cups of water. Add your dried chiles (wear gloves!) that have had the stems and seeds removed to a large bowl. Cover with boiling water and weigh down with another plate to ensure they are fully submerged. Allow to soak for at least 30 minutes.
Transfer softened chiles along with 1 ½ cups of the soaking water and the chopped garlic to a blender. Process until smooth and set aside.
To cook in the crockpot: Cut the pork into bite sized pieces. In a large saute pan, cook the onion and pork on high heat, turning only once, for a total of about 8 minutes to brown. Transfer onion and pork to a slow cooker. Add chicken broth, hominy, salt, and ¼ - ¾ cup of the chile sauce to the slow cooker. If you are unsure about how spicy your sauce is, start out with a small amount. You can always add more. Cook on low 6-8 hours. Shred pork, if desired, before serving.
To cook in the Instant Pot: Brown the whole roast along with the onion for 3-4 minutes on each side in order to get a nice sear. Add all 8 cups of the chicken broth, ¼ - ¾ cup of the chile sauce (again, less is more if it is super spicy), and the salt. Cook on high pressure for 90 minutes. You can slow or quick release the pressure (I usually do quick release because I'm in a hurry). Remove the meat and transfer it to a cutting board. When cool enough to handle, shred the meat, discard the fat, and add the meat back to the soup. Add hominy to the hot broth and allow everything to heat through before serving. Add additional chile sauce and/or salt, to taste.
To serve, top with fresh cilantro, avocado, chopped radishes, shredded cheese, and additional chile sauce for extra spice.