1. Preheat oven to 350°F (175°C).
2. In a large pot, add beef broth and bring to a boil. Add guajillo and ancho chilies, then remove from heat and let them soak for 20 minutes.
3. In a blender, combine soaked chilies, onion, garlic, oregano, cumin, and a cup of the soaking liquid. Blend until smooth.
4. Season beef chunks with salt and pepper. In the same large pot, heat some oil over medium-high heat. Brown the beef on all sides.
5. Pour the chili sauce over the beef. Add bay leaves and remaining beef broth. Bring to a boil.
6. Cover the pot and transfer to the preheated oven. Cook for about 3 hours or until the beef is tender and shreds easily.
7. Remove bay leaves. Shred the beef using two forks. Serve with warm tortillas and your favorite toppings.