So I actually went online and found Andes peppermint chips, and then re-rolled the darn things. It's been a day, and there's no sign of sludge, so I think we're okay now. But I am not sure I'm going to make this recipe again -- frustrating!
Peppermint bark next year, perhaps. Or squares of peppermint fudge. Something else. These are just fine, now that I'm using the right stuff, but I feel traumatized by my truffles.