In a large pot, bring water to a boil with the tomatoes, onion, garlic, serrano pepper, and a pinch of salt.

Once boiling, add the beef shank, soup bone, bay leaves, and black pepper to taste.

Boil for 2 hours or until the meat is very tender.

Finely chop the cabbage, cilantro, and onion, and set aside.

When the meat is tender enough to shred with a fork, turn off the heat, shred the meat, and set it aside in a smaller pot or skillet.

Blend the vegetables used to cook the meat and return them to the remaining broth.

Add 1 beef bouillon cube and boil over high heat.

Assemble the tacos with the meat and vegetables, and serve with the broth (consommé) where the meat was cooked.