I will be slow roasting a whole pork shoulder tomorrow -- it's huge!  For most of the time the oven will be set to a fairly low temperature and the joint will be covered with foil.  However for a time I will remove the foil and turn the oven up to full temperature to get some good crunchy crackling developing.  My question is: should I do this crackling at the beginning or the end of the roasting? 
This is the way I've always done it...  I like to give the shoulder a good blast at a high temperature at the beginining to get some good colour and add flavour. Score the skin, season with salt and give it about half an hour at 220 degrees C or higher, uncovered, with some stock veg in the tray. Take it out, add some herbs or flavourings if you like (bay leaves, lemon, thyme, spices etc) pour in half a bottle of wine and about the same in water. Cover the shoulder in a sheet of baking paper, then cover tightly with foil (occasionally foil will stick to the fat on the pork, so it's best to have a layer of parchment between).  After it's slow cooked at the low temp and is falling apart tender, take it out and turn up the oven again. Strain off all the juices for making your sauce, then carefully remove the skin and lay it on a seperate, dry, tray and give it a blast in the hot oven .   This has always worked for me as you're getting perfect meat and perfect crackling. Slow cooking meat always makes the skin flabby and if it's a joint as large as a shoulder I'd prefer to remove the skin and blast it at the end on it's own rather than still on the joint as you run the risk of drying some of the meat in the process of drying the skin enough for it to crackle.  Hmm... crackling.... 