Optional: In a large skillet over medium heat, sear the beef chuck roast chunks for 3-4 minutes on each side until browned. Remove from heat and set aside.
In a blender, combine the guajillo and ancho peppers with a splash of beef broth. Blend until smooth, adding more broth if needed to help with blending.
In the crockpot, add the chopped onion, minced garlic, cumin, oregano, black pepper, salt, beef broth, apple cider vinegar, lime juice, and bay leaves.
Add the seared beef chunks (or raw if you skipped searing) and pour the blended pepper sauce over the top. Stir to ensure the beef is well coated with the spices and sauce.
Cover the crockpot and cook on low heat for 8 hours, or until the beef is tender and easily shredded.
Once cooked, remove the bay leaves and shred the beef with two forks inside the crockpot. Mix well to absorb the sauce.
Serve the birria in bowls with fresh cilantro as a garnish, along with corn tortillas on the side for tacos.