In a dry skillet over medium heat, toast the dried guajillo and ancho chiles until they become fragrant, about 2-3 minutes.

Transfer the toasted chiles to a blender with the onion, garlic, cumin, oregano, and about a cup of beef broth. Blend until smooth, adding more broth if necessary.

In a large pot or Dutch oven, heat some oil over medium-high heat and sear the beef on all sides until browned.

Pour the chili sauce over the beef and add the remaining broth. Bring to a boil, then reduce the heat, cover, and let it simmer for about 2-3 hours, or until the meat is fork-tender.

Once tender, remove the beef from the pot, shred it, and return it to the pot to soak up the broth.

Warm the corn tortillas in a hot skillet for a few seconds on each side.

Fill the warm tortillas with the shredded beef and top with cilantro and diced onions. Serve with lime wedges and a bowl of the broth for dipping.