There's a video series by Leslie Lamport himself: https://lamport.azurewebsites.net/video/videos.html

There's also Dr. TLA+ series by Microsoft Research at https://www.youtube.com/watch?v=ao58xine3jM&list=PLD7HFcN7LX...

You can watch Leslie Lamport himself explaining it at https://lamport.azurewebsites.net/video/videos.html . It doesn't cover Pluscal, but goes deep into TLA+.

(BTW count the different shirts).