If I may offer a different perspective, I enjoy the mystery of a great dish and leave it be without trying to recreate. More often than not it does lead to some frustration. Why not honor this pub and take your friends there to see for themselves how good it is. You will be patronizing the spot and garnering favor with the owners which may lead a a free drink at some point. If you want to host a dinner make something you are good at and leave this special sauce to them. Just my two cents.