The MSF’s “Motorcycling Excellence” book. You can order from MSF directly, or get it on Amazon.
Covers pretty much everything in the BRC, in greater depth (e.g. there’s a whole chapter on countersteer), plus some more advanced riding techniques toward the end. Also cool are the assorted little vingettes on various topics from different motorcycle professionals (former racing champs, motorcycle engineers, instructional school owners, etc.).
It’s a good basic reference tool for new riders, and much nicer than the cheap booklet you get at the BRC.