Cover the chiles with water and simmer for 15 minutes until they are soft.
Puree chiles in a blender along with the water until smooth.
Brown the pork in the oil. Add onion and garlic and sauté until soft. Add
flour and quickly brown, being careful that it does not burn. Add the chile
puree and tomatoes, bring to a boil, reduce the heat, and simmer for 15 minutes.
Add the beef stock and oregano. Cover the pan and simmer until the meat
is tender, about 1 1/2 hours. The meat should be tender and the gravy quite