Perfect crackling is the holy grail of Sunday lunches, and this method guarantees it every time. The spice combination was inspired by a trip to Istanbul, where I had cumin smoked fish, and the aroma that wafts from the oven after the first couple of hours transports me back there immediately. Still, all you need to know is that the crackling is crackly, the pork is juicy and, not having to peel the squash, this roast dinner could barely be less work.