16 corn tortillas (6-inch), lightly toasted (we used hard tacos)
preheat oven to 350 degrees. in a heavy pot with a tight-fitting lid, stir together chiles, ketchup, 1 cup water, garlic, oregano, 2 teaspoons salt, and 1/4 teaspoon pepper.cut beef into 4 equal pieces. add to pot, and turn to coat. cover, and bring to a boil; transfer pot to oven. bake, covered, until beef is fork-tender, about 2 1/2 hours.transfer beef to a bowl. with a large spoon, skim off and discard fat from cooking liquid. shred beef with two forks; moisten with cooking liquid as needed. season with salt and pepper. serve beef with tortillas and desired toppings.
I don't currently have a cast iron pot so I used my stoneware piece instead and covered it with foil. and it worked like a dream.