Remove the stems and seeds from the dried guajillo and ancho chilies. Place the chilies in a bowl and cover them with hot water. Let them soak for about 15 minutes, or until they soften.

Add the softened chilies, chopped onion, garlic cloves, and diced tomatoes to a blender. Blend until the mixture is smooth. Add a small splash of beef broth if needed to help everything blend together.

Cut the beef chuck roast into large chunks and place them in the crockpot. Pour the blended chili sauce over the beef, then add the beef broth, vinegar, oregano, cumin, bay leaves, salt, and pepper.

Cover and cook on low for 8 to 10 hours, or until the beef is very tender and pulls apart easily with a fork. Remove and discard the bay leaves.

Shred the beef using two forks, then stir it back into the sauce. Let the shredded beef sit in the sauce for a few minutes so it can absorb more flavor. Taste and adjust the seasoning if needed.

Heat a small amount of oil in a skillet over medium heat. Lightly dip each corn tortilla into the birria sauce, then place it in the hot skillet. Add shredded beef to one side of the tortilla, fold it over, and cook until crispy.

Flip the taco and cook the other side until golden and crisp. Repeat with the remaining tortillas and beef.

Serve the tacos hot with extra birria sauce on the side for dipping. Add onion, cilantro, lime, or your favorite toppings if desired.