Season all sides of the chuck roast with salt and pepper and preheat a cast iron skillet over medium high heat.
Add the oil and once hot, sear the meat for 4-5 minutes on all sides.
Next, add guajillo chiles, arbol chiles, chipotle peppers, onion, garlic, beef stock, tomato paste, diced tomatoes, lime juice, cumin, thyme, oregano, cinnamon sticks, bay leaves, cloves, paprika, minced dried onion, and coriander to the crock pot. Stir to combine.
Place chuck roast into the crock pot and cover. Cook for 9-10 hours on low.
Remove the chuck roast from the crock pot and place into a bowl. Shred using 2 forks.
Remove and discard the bay leaves and cinnamon sticks. Take the stems off the peppers and discard.
Next, use an immersion blender to blend sauce until smooth. (Use a food processor or stand blender if you do not have an immersion blender and return to the slow cooker or transfer to a large bowl.)
Add 1 cup of sauce to the bowl with the shredded meat and stir to coat.
Assembling the Tacos
Heat a frying pan over medium high heat and once hot, add cooking oil to the pan.
Using a pair of tongs, dip each side of the tortilla in the sauce and then double them for frying.
Place the dipped, now doubled tortillas into a frying pan flatly and fry for about two minutes.
Flip, add a bit of sauce, the meat, onions, and cilantro to one-half of the tortilla, fold it in half and fry each side of the now shaped taco for up to 2 minutes per side. Spoon a bit of sauce over each side of the tortilla after it’s been fried.
Transfer to a serving plate and serve with a bowl of pureed sauce for dipping. Add additional diced onions and cilantro as a garnish if desired.
Notes
Want queso birria? Simply, add Monterey jack cheese to the tacos after adding the meat while frying.
Store any remaining sauce in an airtight container. Put the beef in a separate container. Keep both in the fridge for up to one week.
Mexican oregano and 'regular' oregano used in Italian dishes are two different herbs from different plants. You can use 'regular' if you can't find Mexican but it will have a slightly different flavor.