How to reminded a Prof of a promised recommendation letter (2 years ago) I am an undergraduate student volunteered at a research lab 2 years ago, working under a phd student. At the end of the work term, the phd student arranged a meeting with the prof so that I presented my work to him. He was rather impressed and promised to provide reference (2 years ago). 

Right now, I am applying graduate studies so I would need his recommendation letter. But the problem is that he might not remember me because I didn't work directly under him and I merely gave a presentation. What kind of approach should I take in order to remind him of this issue?
Write a letter, send an email.

Say, 


  Hello, I am user3222184, and when I was an undergraduate, I
  volunteered at your research lab in 2013. I presented xyz work to you.
  
  I am pursuing graduate studies and would be honored if you can write
  recommendation letter for me.
  
  Thanking you, user3222184