Guanciale is the cheek of the pig which has been cured and air-dried in a similar way to pancetta.  Guanciale has more fat than pancetta, but as a result has a huge depth of flavour.  The fat is transformed by the curing so it becomes silky and unctuous. You haven't truly made carbonara unless you've used guanciale!

Please specify in the comment section whether you would like this product as a whole piece or sliced.