For crackling, should I give pork a blast of super heat at the start or end of roasting? 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?
The heat should be applied at the end, if you covered the crackling with tinfoil and slow cook it will soften (not crispen!) due to the steam and the trapped fat.