Heat a bowl, containing 1 cup water in the microwave to boiling. Fully submerge the chiles in the hot water until well saturated - about 1 hour. With a hand blender, puree the chile/water mixture into a smooth consistency. Strain the paste through a fine-mesh strainer into a bowl. Use a wooden spoon to mash, scrape and coax the maximum quantity of the sauce from the pods. Allow this mixture to cool.
Chop the garlic - finely. Slice the pork butt into 1/2 wide strips. Place the pork strips, garlic, oregano, cumin and salt to taste into the red chile sauce. Marinate the meat, covered, in the refrigerator for 24 hours.
Preheat the oven to 300-325 degrees. Pour the contents of the marinade bowl into a pyrex baking dish. Cover tightly with foil and braise for 3 hours or until extremely tender. Fat will render from the pork. It'll be necessary to skim the fat from the surface of the liquid. Assemble the tender, disintegating tendrils of pork along with sauce and cheese - by wrapping them up in skillet-softened, flour tortillas. Top with sour cream and salsa - if desired.