The pork should be at room temperature before you start this recipe. Using a paper towel dry the pork all over including the skin.
Using a very sharp knife (A Stanley or Craft knife works well) make slashes approx a finger width apart across the skin, don't cut through to the meat, about half way down the fat is good.
Rub the skin with the oil ensuring it goes down into the slashes. Sprinkle with salt, again make sure it is down into the slits.
Place the pork into a large roasting tin. Tuck the two onion halves under the meat, this will help keep the meat upright as well as adding flavour to the meat. Cook for 1 hour and 40 minutes. If you are using a larger or smaller joint then cook for 25 minutes per 450g/1lb, plus add on a further 25 minutes.
Switch off the oven (unless you need to cook the crackling further, see note below). Remove the meat from the roasting tin and place onto a serving plate, cover loosely with foil and place in the oven with the door slightly ajar. If you need to keep the oven hot (ie for cooking potatoes or maybe Yorkshire Puddings then wrap the meat completely in foil and keep in a warm place.
Remove the onion from the pan, then place the pan on the stove top over a high heat until the meat juices begin to bubble but not burning. Add the flour, and stir to blend into the meat juices. Pour in the cider or wine and scrape all the juices from the bottom of the pan, reduce to a sticky glaze. Do not leave the pan unattended as the reduction happens very quickly.
Add the stock and stir well,
Strain the gravy through a fine sieve into a saucepan and reduce by one-third. Add the butter in tiny pieces shaking the pan gently until the all the butter is absorbed. Keep warm until needed.
Remove the crackling from the pork and carve into thick slices.
Serve with pieces of crackling and the gravy, seasonal vegetables, Apple Sauce is a great accompaniment as is Sage and Onion Stuffing. Don't forget the traditional Yorkshire Puddings if it is a Sunday lunch.
