Heat the oven to 220°C. For the best crackling, the oven needs to be really hot when you put the meat in.
Dry the meat very thoroughly all over with kitchen paper.
Slather it with olive oil (the easiest way to do this is with your hands) and give it a good sprinkling of sea salt.
Sit it on a sprig of rosemary in a roasting tin and roast for 45 minutes.
Baste and turn the oven down to 180°C.
Roast for 15 minutes at 180°C and then for a final 15 minutes at 220°C (check that the crackling isn’t burning before turning the oven up for the final 15 minutes – you may need to leave it at the lower temperature for slightly longer).
Meanwhile cut the rhubarb into 1″ pieces and peel the shallots (leave them whole). Peel and grate the ginger and peel and chop the garlic.
When the meat is cooked, dish it up onto a warmed plate and leave to rest, covered loosely with a clean tea towel. Tip off most of the fat (and keep it in the fridge for roast potatoes) and remove the rosemary.
Return the roasting pan to the oven with the shallots for 5 minutes.
Turn the shallots so that they caramelise all over and then add the rhubarb, sugar and garlic.
Cook for another 5-10 minutes. Keep a watch – you don’t want the rhubarb to collapse or the garlic to burn.
Remove the rhubarb and shallots carefully with a slotted spoon and put them round the meat.
Deglaze the pan with the stock (or water), add the Ginger Wine and the grated ginger and reduce by a third. Add the knob of butter, adjust the seasoning and also the sweetness – if the rhubarb is young and pink you will not need any more sugar (the wine is sweet). Strain the sauce over the shallots and rhubarb and serve.