A fake pudding invented to make the English appear ignorant about the shit house local recipes. When mentioned they commonly reject it's existence then agree it does just to sound less stupid.
It is also a term for when a gay man falls asleep with jizz on his face and it dries so he can chip it off and eat it when he is hungry.
Q: "Hey John, is that Hastings Pudding on your face?"
A: "Fook me I have been looking for that cunt on google for ages, fookin takes good!!"