Toast the dried guajillo and ancho chilies in a dry skillet over medium heat for 1 to 2 minutes per side, until fragrant, then soak in hot water for 10 minutes until pliable.

Drain the chilies and blend with the onion quarters, garlic, tomatoes, vinegar, cumin, oregano and 1 cup of beef broth until smooth.

Place the beef chunks in a 6-quart crockpot, pour the chili sauce and remaining 3 cups of broth over, and add the bay leaves and cinnamon stick.

Cover and cook on low for 8 hours, until the beef shreds easily with two forks.

Remove the beef, shred it, and discard the bay leaves and cinnamon stick.

Skim the fat from the broth and set it aside; return the shredded beef to the crockpot on warm.

Dip each tortilla in the reserved fat, fill with beef and cheese, fold in half, and pan-fry on a hot griddle for 2 minutes per side, until crisp and the cheese melts.

Serve with diced onion, cilantro, lime wedges and a small cup of the warm broth for dipping.