Pour the vinegar and lime juice into a large bowl (it should be able to hold all the beef ). Whisk in the chipotle paste, garlic, spices, herbs, sugar and some seasoning. Mix in the beef, ensuring it’s well-coated, then cover and leave to marinate for 1-2 hrs, or chill overnight.
Heat the oven to 160C/140C fan/ gas 3. Put the beef on a plate, then tip the marinade into an ovenproof casserole, along with any bits that have stuck to the bowl. Pour in the stock and bring to a simmer. Add the beef and simmer for 1 min, then cover and cook in the oven for 2 hrs.
If the beef isn’t tender enough to shred, cook for 15 mins more, then check again. Leave until cool enough to handle, then lift onto a board using a slotted spoon. Bring the sauce to the boil and reduce to about 300ml. Meanwhile, roughly shred the beef, discarding any fat or gristle. Stir back into the sauce to reheat, then serve in the casserole dish with the tacos, coriander and toppings on the side for everyone to help themselves.