Prepare the Chiles: In a small pan over medium heat, lightly toast the guajillo and ancho chilies for about 2-3 minutes until fragrant. Be careful not to burn them. Once toasted, soak them in hot water for about 15 minutes until softened, then drain.
Blend the Sauce: In a blender, add softened chilies, quartered onion, minced garlic, ground cumin, oregano, smoked paprika, and 1 cup of beef broth. Blend until smooth. Add salt and pepper to taste.
Cook the Meat: In a large pot or Dutch oven, add the beef chunks, the blended chili sauce, remaining beef broth, and apple cider vinegar. Bring to a simmer over medium-high heat, then reduce to low. Cover and let cook for about 2.5 to 3 hours, or until the meat is tender and shreds easily.
Shred and Strain: Once the beef is cooked, remove it from the pot and shred it with two forks. Strain the remaining broth, discarding any solids. Return shredded meat to the pot and mix with some of the broth for added flavor.
Prepare Tacos: In a skillet over medium heat, slightly toast corn tortillas on both sides. Assemble the tacos by filling them with the shredded beef mixture.
Serve: Garnish your tacos with chopped cilantro, diced onions, and serve with lime wedges on the side for squeezing fresh juice on top.