Although there are many books about Johann Sebastian Bach, one of my favorites is Evening in the Palace of Reason: Bach Meets Frederick the Great in the Age of Enlightenment, by James R. Gaines. I read it recently for the second time and already want to read it again. Here’s The New York Times’ Sunday Book Review from 2005.
I’ve also recently discovered a book on Bach written by the English conductor and early music scholar, John Eliot Gardiner. Entitled Bach: Music in the Castle of Heaven, it was published in late 2013. According to this NYT review of the book, Gardiner paints the picture of Bach as both man and musician, "warts and all." I plan to dive in straightaway.
Both books are sure to warm up many a long winter’s night!