Season the short ribs with salt and pepper up to 24 hours in advance. In a large dutch oven over medium heat, add avocado oil, and working in batches, sear all sides of the short ribs until golden brown and remove.
Add the onions to the pot and saute until cooked through, salting as you go, around 5 minutes. Add the garlic, tomatoes, bay leaves, guajillo peppers, chicken stock, oregano, cumin and season with salt. Taste to make sure the seasoning is correct and adjust as needed. Add the short ribs back to the pot, making sure they ¾ covered by liquid. Bring up to a low simmer and add a lid, simmer on low for 2 hours, or until the short ribs are easily shreddable, and falling off the bone. If they are still tough, keep simmering until they are fork tender.
Remove the short ribs and shred with forks, set aside.
Remove the gaujillo peppers from the liquid and blend in a blender, adding some of the chicken stock to blend. Stir the blended peppers back into the broth. Remove any bay leaves, then with an immersion blender, blend the liquid until smooth.
Add the shredded meat to a large pot or pan, and cover with about ⅓ of the liquid. Bring up to a simmer and reduce the liquid with the beef until it is thick and saucey.
Save the extra sauce for dipping tortillas or just dipping tacos into! Serve and enjoy!
