Provided by the rather talented Jeff Mallow, in his own words:

Well the first song that comes to mind is Bonnie Raitt doing I Can’t Make You Love Me If You Don’t. Not sure that it was her song originally but she destroyed it in the best possible way.
Jeff Mallow - Composer

I've had this on repeat while I build this page - I didn't know the track before Jeff recommended it.  

If someone could unlock the formula behind what makes a classic..., we'd all be screwed!

This is a beautiful song.

Jeff Mallow is a composer of music for film, Television and Advertising.  Past works for NBC, American World Pictures, National Geographic, Universal Networks International, SyFy...

Quick note from the Musicto team - If you get a chance to work with Jeff, do it.  Andrew was lucky enough to work with him for a year or so..., he's a cat.