In 1489, a magnificent illustrated Passover Haggadah was sent as a bequest to the Monastery of Saint Quirinus at Tegernsee in southern Germany. Shortly afterwards, the monastery's librarian sent the book to a Dominican friar named Erhard von Pappenheim, a Hebraist and expert on Jewish practice, and asked him to write a prologue. In response, Erhard wrote a remarkable treatise that is arguably the earliest quasi-ethnographic account of Jewish practice...