It's pub grub at its finest, as Polly clues Jack up on all there is to know about sausage and mash. We find out why the nickname of 'the banger' is so appropriate and how the potato came to be the carb-accompaniment of choice. Back in his Cornwall kitchen, Jack dishes up a very indulgent mash and gives us some secret twists for the perfect gravy; soy sauce, Worcester sauce, miso paste, ketchup and yeast extract.