Preparation:

• Preheat the oven to 130°C.
• Season the beef shin well with salt and pepper. Heat the oil in a large cast-iron pan (use one with a lid) over medium-high heat. Working in batches so as not to crowd the pan, sear the beef  until well browned all over, 6–7 minutes per batch.
• Remove the meat with a slotted spoon and set aside between batches.
• When all the meat is cooked, add all the meat to the pan with the onion, garlic, and all the other ingredients except the chocolate. Pour in just enough water to halfway cover the meat.
• Bring to the boil, cover with the lid and place in the oven. Leave to braise for 7–9 hours, preferably overnight.
• Using a slotted spoon, remove the shin from the pan and set aside to cool. Put the pan on the hob over medium heat and cook, stirring, to reduce.
• Add the chocolate in small pieces.
• Remove the beef from the bone, pull into bite-sized strips with your hands and add to the sauce.
• Crisp the tortillas in a hot pan according to the instructions on the packet.
• To serve, put some of the braised beef on each tortilla, top with onion, coriander, jalapeño peppers and cheese and season with a squeeze of lime juice. Eat with your hands!