In a dry skillet over medium heat, carefully toast the guajillo and ancho chiles for 1-2 minutes, turning occasionally, until they become fragrant but do not burn. Once toasted, remove from heat and allow them to cool slightly. Transfer the cooled chiles to a blender.
In the blender with the chiles, add the quartered onion, minced garlic, ground cumin, oregano, smoked paprika, cinnamon, apple cider vinegar, and 1 cup of beef broth. Blend the mixture until it reaches a smooth consistency.
In a large mixing bowl, generously season the beef chunks with salt and freshly ground black pepper to ensure even flavor throughout the meat.
In a crockpot, place the seasoned beef chunks. Pour the blended sauce over the meat, ensuring it is evenly coated. Add the remaining 3 cups of beef broth, making sure the meat is submerged for maximum flavor absorption.
Cover the crockpot and cook on low for 8 hours, or on high for 4-5 hours, until the beef is fork-tender and easily shreds apart.
Once the cooking time has elapsed, carefully remove the beef from the crockpot using tongs and place it on a cutting board. Use two forks to shred the meat into bite-sized pieces.
In a skillet over medium heat, lightly warm the corn tortillas for about 30 seconds on each side, or until they are pliable and slightly toasted.
Take a warm tortilla and place a generous amount of the shredded beef in the center.
Top each taco with freshly chopped cilantro. Serve with lime wedges on the side, and for an extra kick of flavor, drizzle some of the rich broth from the crockpot over the tacos before enjoying.
Notes
Serve the tacos on a large platter, with lime wedges and a small bowl of broth for dipping. Consider adding thinly sliced radishes for a pop of color and crunch!