Combine all the marinade ingredients in a large lidded casserole dish. Heat the sunflower oil in a large heavy-based frying pan until practically smoking and fry the pork until a dark brown all over. Add the pork to the marinade and leave to marinate in the fridge for 24 hrs.
The next day, heat oven to 180C/fan 160C/gas 4. Remove the pork from the marinade and set aside. Place the marinade over a high flame and bring to the boil. Boil for 15 mins, skimming off any foam from the surface. Add the stock and bring back to the boil, then add the meat. Put on the lid, or tightly cover the casserole with foil, and put into the oven to cook for 3 hrs turning the meat halfway through.
Lift out the pork and keep somewhere warm. Strain the cooking liquid through a fine sieve
into a clean pan. Bring to the boil, then boil to reduce for about 15-20 mins. Check the seasoning before serving with the gravy.