Preheat a large heavy casserole over medium-high heat. Once hot, add the pork pieces, sprinkle 1 teaspoon salt, and cook for 15 minutes, stirring as it starts to brown. Reduce heat to medium, pour in 5 cups of water, cover and cook for another hour and a half.

Meanwhile, place the guajillo chiles, bay leaves, and garlic in a medium pot, cover with water and bring to a boil. Simmer over medium heat for 10 to 12 minutes until the chiles are completely rehydrated and plumped up.

Place rehydrated guajillos, garlic, and bay leaves in the jar of a blender, along with 1 cup of the cooking liquid, and the oregano, coriander seeds, remaining ½ teaspoon salt, black pepper, cumin, and vinegar. Puree until completely smooth.

Pour the chile puree onto the meat, mix well, and continue to cook, partially covered, for another 10 to 15 minutes. Stir energetically, but occasionally. By the end, the meat should be so tender and luscious that it falls apart completely and will break into very thin and almost shredded pieces. Turn off the heat.

This is the prepared chilorio base. You can let it cool and scrape into a colander, set over a bowl or pot, to drain the fat. Reserve the fat for later use. You can refrigerate the chilorio and the fat until ready to use.

If you are ready to eat it, set a casserole over medium heat, add a tablespoon or two of the reserved fat from the chilorio. Once hot, add the onion, Anaheim chiles, and tomatoes, stir and cook for 8 to 9 minutes until softened. Add the chilorio, mix well, and continue to cook for 10 more minutes.

Serve with flour or corn tortillas or use for any other type of filling or dish (such as pasta, lasagna, tortas, sandwiches, burritos).