Maybe I'm Amazed" from his first solo album. It's a rare combination of tone and passion that you so rarely hear these days.
Here are some things to listen for:
1. There's a very subtle effect on Paul's voice. I'm told that he favors a 175 millisecond delay on his vocals both in the studio and live, and you can hear it here, with a little bit of a short reverb tail on the delay as well.
2. The background vocals are Paul and Linda McCartney in a fairly open harmony, and have a more of the short reverb to push it back in the mix.
3. Check out Paul scatting during the guitar solo, which are mixed very low on the final mix.
4. It sounds like Paul did the vocal live while cutting the piano, then overdubbed the vocal on the last verse at 2:04 as the piano leakage changes.
All in all, this is one amazing vocal recorded when Paul was at the very top of his game.