Judaism, Sufism, and the Pietists of Medieval Egypt: A Study of Abraham Maimonides and His Times by Elisha Russ-Fishbane (New York: Oxford University Press, 2015). I couldn't believe that no-one had done a proper book on this amazing episode (discussed in chapter 3 of Western Sufism) and here it is--the proper book.
The book has six chapters, divided into three chapters. First come social foundations ("The Making of a Movement" and "Ideals and Institutions"), and then prayer ("The Devotional Life" and "Prayer Reforms"), including adoption and adaption of Sufi forms. The book ends with prophecy and messianism ("The Return of Prophecy" and "From Prophecy to Redemption"). The prophecy is, essentially, the consequence of union, making the completed man (al-insan al-kamil) into a [lesser] prophet, and messianism or redemption was, in some ways, the logical consequence.
Well-researched and well-written.