Prepare the Birria: In a crockpot, add the beef, onion, garlic cloves, bay leaves, salt, pepper, chili powder, cumin, oregano, thyme, garlic powder, allspice, and adobo seasoning. Pour in the beef broth and add water until the ingredients are fully covered.
Prepare the Chiles: Remove the stems and seeds from the guajillo and chiles de árbol. Rinse them, then boil in water for about 5 minutes until softened. Add the softened chiles to a blender with half a tomato and some of the boiling water. Blend until smooth, then add this mixture to the crockpot.
Cook the Birria: Set the crockpot to low for 8 hours (or high for 4 hours). Cooking on low will yield more tender meat.
Shred the Meat: After cooking, shred the meat directly in the crockpot or remove it and shred with a fork. Save the consommé (broth) to use for dipping.
Make the Tacos: Dip tortillas into the consommé, fill with cheese and the shredded Birria meat, and fry in a skillet until golden and crispy on both sides. Top with fresh cilantro and onions.
Serve: Serve the tacos hot with a side of the reserved consommé for dipping. Enjoy!