To create the Tastiest Beef Birria Tacos, follow these simple steps:

1. Prepare the Chilies: Soak the guajillo and pasilla chilies in hot water for about 15 minutes until soft. Drain and set aside.

2. Blend the Sauce: In a blender, combine the soaked chilies, chopped onion, minced garlic, cumin, oregano, smoked paprika, black pepper, and salt. Add a cup of beef broth and blend until smooth.

3. Sear the Beef: In a large pot, heat a couple of tablespoons of oil over medium-high heat. Sear the beef chuck roast on all sides until browned.

4. Combine Ingredients: Once the beef is seared, pour the blended sauce over it. Add the remaining beef broth and apple cider vinegar.

5. Simmer: Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for approximately 3 hours or until the beef is fork-tender.

6. Shred the Beef: Once cooked, remove the beef from the pot and shred it using two forks. Return the shredded beef to the pot, stirring to coat in the broth.

7. Warm the Tortillas: In a separate skillet, warm the corn tortillas over medium heat until pliable, about 30 seconds per side.

8. Assemble Tacos: Fill each tortilla with a generous amount of shredded beef, then top with chopped onions and cilantro to taste.

9. Serve: Ladle some of the broth from the pot into small bowls for dipping.