Plovnik, History of?

I am participating in testing recipes for the New York Jewish Bakers Book. One of the recipes that I baked was the "Plovnik, or Black Bread".

This was such an intriguing recipe, with strong, rich flavors, that I wanted to get some more information about it.

My first stop when looking for information is, of course, GOOGLE. The only hits are linked back here. I have found loads of stuff on Black Bread, but no Plovnik.

Anyone got anything on this Beautiful Bully of my Taste Buds??