ASM wrote:

What would be the best book explaining mountain flying???

Jochen von Kalckreuth: Segeln über den Alpen

It's somewhat vintage, but still fully valid. For me this is the
definitive book about soaring in the mountains. The book focuses on the
alps, but the knowledge it teaches can be used in any mountains. One
possible caveat, though: It's German. (I don't know whether there's a
translation)