Ingredients
1-1.5kg/2lb 4oz-3lb 5oz boned pork loin, trimmed of most of its fat, or lean belly, skin off
salt and freshly ground black pepper
2 tbsp olive oil
75g butter
2 medium red onions, halved and thinly sliced
4 sprigs fresh thyme, or pinch dried thyme
2 bay leaves
300ml/10fl oz Pedro Ximénez or sweet oloroso sherry
100ml/3½fl oz sherry vinegar
100g/3½oz raisins

Method
1. Season the pork with salt and freshly ground black pepper. Place a large saucepan over a medium heat and add the olive oil. When hot, lower the pork into the pan and sear until just golden brown on all sides and both ends.
2. Remove the pork and set aside briefly. Still over a medium heat, add the butter and, when it foams, the onions with a pinch of salt. Fry for ten minutes until sweet, stirring occasionally.
3. Pour off any excess oil, then add the thyme, bay leaves, sherry, sherry vinegar and raisins and turn the heat to low.
4. Return the pork to the pan, cover with greaseproof paper or kitchen foil and put the lid on. Cook slowly for 1-1¼ hours or until the meat is just cooked through but still juicy, turning occasionally, so it cooks evenly. To determine whether the pork is cooked, gently push a sharp knife or metal skewer into the centre of the meat. Count to ten and pull out. Touch the area above your top lip gently with the end of the skewer. If it is hot, the meat is cooked.
5. If using belly pork, double the cooking time, or cook until tender. Make sure the juices do not simmer dry. Just add a little water from time to time.
6. Let the pork rest for ten minutes, covered loosely with foil, before slicing.
7. Turn the heat under the sauce to high and reduce it for five minutes, until it is still runny but delicious. Taste the sauce and adjust the seasoning if necessary. Serve.