My prof asked me the same thing. Here's what I gave him:
- Briefly explain your position at --school--
- Explain how long you’ve known me and in what capacity
- Choose two or three qualities that describe your opinion of me. This could include evaluation of my abilities at writing, organizing, understanding abstract concepts, communication, and my diligence, perseverance, and determination.
- It should highlight why you feel this way about me, with a few details
- It could assess my character on a more personal level like my honesty, leadership, maturity level or something more personality-oriented (like my winning smile)
- It could give a benchmark for comparing me to others with whom you’ve worked (“Newy is the coolest ever!!!”)
- Because of all these reasons, you think that I will make valuable contributions to my law school and that I have the potential to be a great lawyer or something like this…
I think having an A- is no big deal at all, same with the prof being from your minor. The most important thing is that the prof can describe your qualifications and justify their description with examples. This is what I've gathered from my research.
Good luck to you...
Edit: Be sure to tell them up front not to open the letter "Dear LSAC"