In a dry skillet, toast the guajillo and ancho chiles until fragrant, about 2-3 minutes. Remove from heat and soak in hot water for 15 minutes.

In a blender, combine the soaked chiles, cumin, oregano, garlic, black pepper, salt, beef broth, and apple cider vinegar. Blend until smooth.

In a large bowl, combine the beef chuck roast and bone-in beef shank with the marinade. Cover and refrigerate for at least 2 hours, preferably overnight.

Preheat the Dutch oven over medium heat. Add the marinated meat and any remaining marinade. Cover and cook on low for about 4 hours, or until the meat is tender and easily shredded.

Shred the meat and serve in bowls with the broth. Top with chopped onion, cilantro, and lime wedges. Serve with warm corn tortillas.