This can be made with pork or beef. As a matter of fact, I think this is the first time I've ever had it with pork. I adapted this recipe and it made enough for 3-4 people, next time I will definitely double the amount of meat so I can have some leftovers.
~2 lb pork roast, cut into 1" cubes
1 yellow onion, chopped
5 cloves of garlic
3 dried ancho chiles
2 dried guajillo chiles
2 cups chicken broth (homemade or reduced sodium!)
1 cup water
2 T preferred fat for cooking
Put pork, 1/2 the onion, and 2 cloves of garlic into a large pot/dutch oven. Add just enough water to cover the meat, and add ~ 1 tsp of salt. Bring to a boil then reduce heat to medium low and simmer partially covered anywhere from 60-90 minutes. You want to cook it until the pork is tender enough to cut with a spoon.
While the pork is cooking, bring the chicken broth and water to a boil. Turn off the heat and add the dried chiles. Cover and let sit for 20-30 minutes until the chiles soften a bit. When they are cool enough to handle remove the stems and seeds. Don't worry if some of the seeds remain, these chiles are pretty mild. Put the chiles in a blender or food processor with their cooking liquid and a couple of pinches of salt and puree until smooth.
Once the pork is done I transfer it along with the cooking liquid to a bowl, and use the same pot to sautee the remaining 1/2 onion and 3 cloves of garlic (chopped) in your fat of choice. After a couple of minutes use a slotted spoon to add the pork back into the pot and cook for 5 minutes more. Then dump in the chile mixture and use the reserved pork cooking liquid to thin the sauce to whatever consistency you like. Cover and simmer for 20-30 minutes. Then eat!
I just had a bowl of this and a spinach salad for dinner. I imagine this could easily be made in a crock pot by making the chile mixture and pouring it over the pork, onion, and garlic; then adding enough water to completely cover the meat. Cook on high for 5 hours, or low for 8 hours. Seems like it would work!