The True Dharma Eye: Zen Master Dogen's Three Hundred Koans,
Translated by Kazuaki Tanahashi and John Daido Loori
The notion that koans don't belong to the Soto Zen tradition can't withstand the fact that Soto's founder, Eihei Dogen (1200-1253), compiled this monumental collection.
Dogen collected the three hundred koans contained in this work called in Japanese Shobogenzo (not to be confused with that other, more famous Shobogenzo he's known for) during his famous travels in China between 1223 and 1227, and it remained in obscurity for centuries-until its discovery in 1934.
It's unlike the other great koan collections in that it's just the koans themselves, without the traditional titles, commentaries, and capping verses-but these are supplied here by Dogen's dharma descendant John Daido Loori, making this a "new entry into this profound and ancient practice" (Tricycle).