Steve Martin / Noam Pikelny on Letterman 2 Years, 7 Months ago
Letterman had Steve Martin on Friday 11/5, and he talked about the first annual Steve Martin Award for Banjo Excellence (or something to that effect). The prize was awarded by a jury convened by Steve, and including Bela Fleck and Tony Trischka among others and presented to Noam Pikelny of the Punch Brothers. Steve and Noam did a dueling banjos bit where Noam took off on a pretty slick scale run. Letterman had the Punch Brothers out as the closing musical act.
Letterman wanted to talk about ANYTHING but banjo or bluegrass, but Martin persisted.
Punch Brothers were a bit "non-traditional" in their bit, but lots of talent there.
It's on YouTube if you search "Steve Martin Noam Letterman" you'll find it.