Roast pork with cider sauce

1) Preheat the oven at the highest setting.
2) While the oven is preheating, score the skin of the pork.
3) Put the pork in a roasting tin, skin side up and rub all over with about 1 tbsp of sea salt.
4) Cut the onion in half and wedge under the pork.
5) Roast in the oven for 25 minutes.
6) Turn the heat down to 190C/375F/Gas 5, and cook for a further 2½ hours.
7) When the pork is cooked remove it from the oven and rest for 30 minutes before carving.
8) Meanwhile tilt the tin and spoon all the fat off, leaving only the juices.
9) Place the roasting tin over direct heat, turned to low, sprinkle in the flour and quickly work it into the juices with a wooden spoon.
10) Now turn the heat up to medium and gradually add the cider and the stock, whisk until is smooth. Season to taste.
11) Sieve and pour the gravy into a warmed serving jug.
12) Carve the pork in to slices and serve with the cider gravy.