This is based upon himmel und erder, a popular German dish. According to my mate, Steve Claydon, who is a huge fan, the soft, silky black pudding is the heaven (himmel) upon the earth (erder) of crushed up apples and potatoes. Until recently, the closest I could find to the German soft black pudding was Spanish morcilla, which works pretty well. Then Peter Gott of Sillfield Farm in the Lake District kindly developed a soft version of his black pudding for me, which is perfect. You can buy it from Borough Market, though you may well have a local butcher who makes something similar and you can soften it up as suggested if necessary. Wrapping the pudding in pig’s caul stops it bursting during cooking.