1. If you can’t buy rindless pork joint trim it yourself: cut off the strings, trim the rind and most of the white fat with a sharp knife and re-roll it, tying up with kitchen string in three or four places. It’s fine to leave it unrolled but it will help keep the meat in one piece when you get to turning it in the braise.
2. Salt the pork generously with salt as early as you can; a day ahead is best.
3. Peel and slice the onions, trim the bottom of the garlic head and halve it horizontally (no need to peel it as the skins will get strained); top and seed the chilies.
4. When ready to cook, heat up a large cast iron casserole or oven-proof pot over medium-high heat and add 2 tbsp. of oil. When it’s hot, brown the meat on all sides; it should take about 15 minutes. Remove the meat from the pan and carefully pour out most of the fat.
5. Return the pan onto the hob and turn the heat down to medium. Add another tablespoon of oil to the pan followed by the onions and garlic. Cook them, stirring often, until softened and slightly browned.
6. Preheat the oven to 160C/300F/gas 3. Add the chilies, bay leaves, tomatoes with all the juice, cumin and paprika to the pan. Place the pork in the middle and add enough beer to come up to almost halfway up the meat. Bring it to a simmer on the hob and transfer to the oven, uncovered.
7. After 30 minutes check that the sauce is only just simmering, and turn over the meat. Turn it again every 30 minutes for the next 3 ½ - 4 hours, topping up the liquid with more beer or just water if it cooks off too much.
8. When ready, the meat should pull apart at the touch of a fork. Carefully remove it from the sauce and leave on a warm plate to rest. Strain the sauce through a colander and bring it to the boil in a clean saucepan. Taste for seasoning and add salt, if necessary and a couple of tablespoons of tomato ketchup if you think it needs a hint of sweetness. Reduce it a little over high heat.
9. To serve, slice the pork across the grain, spoon the sauce over and garnish with chopped coriander and jalapenos.