Remove outer layer from one onion. (The second onion is for the tacos)
Cut the root end off then cut it into fourths.
In a medium pot combine quartered onion, salt, pepper, bay leaves, oregano, whole chillies, garlic cloves, beef broth and beef bouillon.
Over medium high heat, bring to a boil.
Reduce to low and simmer for 10-15 minutes. Stir occasionally.
Let the mixture cool for 5 minutes.
Carefully remove the bay leaves and stems from the chilies.
Using an emersion blender or food processor, blend ingredients together. Mixture will still be hot so use caution.
Place roast in a large slow cooker.
Pour mixture over the top and sprinkle over citric acid or vinegar and stir in.
Place lid on top and cook on low for 8 hours. Or until meat is tender and falls apart.
Once cooked, remove all fat from the roast and shred the beef using two forks.
When ready to serve up, finely dice the second onion (remove the outer layer first), shred the cheese and finely chop the cilantro.
Heat a skillet or pan over medium high heat.
Dip one corn tortilla in the beef consume then place on a hot skillet.
Top with a little shredded cheese, cilantro, onions and a shredded beef.
Fold over and grill on both sides until lightly golden brown and toasted and the cheese is melted.
Repeat with remaining ingredients.
Pour 1/2 cup of consume into a small bowl and sprinkle cilantro and onions on top for every serving.
Dip tacos into the consume.
Serve hot.