Preheat your oven to 240°C/475F/Gas Mark 9.
If the skin on the pork hasn't already been scored, use a sharp paring knife to score the skin into thin strips, ensuring the blade of the knife reaches around halfway through the thickness of the skin.
Place the pork in a roasting tin with the skin facing up and carefully slide the shallots underneath it.
Sprinkle around 1tbsp of sea salt crystals all over the skin, pushing it down between the strips (this helps to make the crackling as crunchy as possible!)
Place the pork onto the top shelf of the oven and roast for 30 minutes to crisp up the skin. Then, turn the temperature down to 190°C/375F/gas 5 and calculate the combined cooking time at 35 minutes to the pound, before deducting the initial 30 minutes cooking time. At this point, I had to cook my pork for a further 1 hour and 50 minutes.
Once cooked, remove the pork from the oven and allow to rest for at least 30 minutes until carving.
As the pork cools, carefully spoon all fat from the surface of the roasting juices and, leaving the shallots in, place the roasting tin over the hob on a low heat, sprinkle in the flour and quickly beat it into the juices using a wooden spoon.
Turning the heat up to medium, slowly add the cider and stock a little at a time and use a whisk to mix into the juices. By now, the gravy should be starting to thicken.
Season the gravy with salt and pepper, remove the shallots and pour into a serving jug. Carve the pork into slices and serve with plenty of crackling and roasted vegetables.