Thanks scooterguy,
That is great advice.
I wasn't sure how that worked or if I should offer to write the letter.
It happened today - my first thought was to send a quick note to the Attending's practice (my rotation ends Friday) but then, I didn't know what to say and I probably won't see them as a rotating student again.
I just started my 3rd year, so it will be year before I need the letter.