Prepare the Chilies: In a dry skillet over medium heat, toast the guajillo, ancho, and pasilla chilies for about 2-3 minutes until fragrant. Be careful not to burn them. Remove from heat and let them cool slightly.
Blend the Marinade: In a blender, combine the toasted chilies, quartered onion, minced garlic, beef broth, cumin, oregano, smoked paprika, salt, black pepper, and cinnamon. Blend until smooth.
Marinate the Beef: In a large bowl, place the beef pieces and pour the chili marinade over them. Add the apple cider vinegar. Ensure the beef is well coated, then cover and let it marinate in the refrigerator for at least 1 hour, or preferably overnight.
Cook in Slow Cooker: Transfer the marinated beef and sauce into a slow cooker. Cover and cook on low for 8 hours or on high for 4 hours, until the beef is tender and easily shredded.
Shred and Serve: Once cooked, remove the beef from the slow cooker and shred it using two forks. Return the shredded beef to the cooker to soak in the sauce for added flavor.
Prepare the Tacos: In a skillet, heat the corn tortillas over medium-high heat for about 30 seconds on each side until warm and slightly crispy.
Assemble the Tacos: Fill each tortilla with a generous amount of the shredded birria, and top with chopped cilantro and diced onions.
Serving Suggestion: Serve the tacos with lime wedges on the side and a small bowl of the strained cooking broth (consomé) for dipping.