I was always fascinated by the dichotomy between Baba-Jaga as the witch in Hansel und Gretel, and as a kind of Frau Holle.
I've been reading Vladimir Propp on this subject: the books "The Russian Fairytale" and "Historical Origins of Fairytales" were very interesting.
Unfortunately, I only have them in Italian translation (and in Russian, but that's not very helpful either).
If you wish I can look up some quotes.