Pha bong kha pa Byams pa bstan ʼdzin ʼphrin las rgya mtsho (David Gonsalez, tr.) The extremely secret Dakini of Naropa: Vajrayogini practice and commentary. Ithaca, N.Y.: Snow Lion Publications, 2011. 408 pp. ISBN 9781559393867. [official site]
From the Blurb
The Extremely Secret Dakini of Naropa is the commentary to the practice of Vajrayogini in the Naro Kacho lineage composed by Kyabje Pabongkha [1874–1941] as revealed to him directly by Vajrayogini herself. This text has become the basis for almost every subsequent Vajrayogini commentary in the Gelug tradition.
Restriction: The material in this book is restricted. This book may be read only by those who have received a Highest Yoga Tantra empowerment. [Unless you are an Indologist, in which case you may consider this requirement beneath you.]