I added a "citation needed" to the following line:

"Not only does it make a wonderful treat for the consumer, but it serves as a powerful and excellent antidote for the chilling, cold effect produced by contact with Dementors, and other particularly nasty forms of Dark magic."

As far as my research can tell, there is no reference to chocolate being useful against Dark magic. It's simply a helpful remedy against a Dementor's nasty habit of sucking the joy out of people. But if there is a canonical source saying otherwise, I think we need that source to be cited here.