To get top quality crackling there’s a few things you have to do. First, make sure the skin is bone dry before you cook your joint. I find slow cook joints like shoulder and leg give the best crackling. Next, score the skin thinly. I do mine with a razor blade. It then needs to be both oiled and well salted, preferably with good, crunchy rock or sea salt.
Get your oven really hot and put the joint on the top shelf for 15 mins, then turn the oven down to low and put the meat on the bottom shelf. Cook it like that for around two and half hours then take it out. Slide a very sharp knife under the skin and separate it from the joint. Scrape out the jelly-like fat, sprinkle some salt in the inside of the crackling and put it back in the oven (skin side down first to dry out the inside) and this time back on the top shelf and turn it back up to high. Keep a close eye on it as can burn quickly at this stage. It takes a bit of effort but this is crackling we’re talking about here. It’s important.
When the inside is dry and crunchy, if the skin side needs a bit longer turn it over and cook for a bit longer. Cool it on a wire rack when it’s done and then get in quick, because if you’re house is anything like mine you have to be if you want to get any.