I thought this was a joke, but then I looked it up on the Star Wars wiki and holy crap it’s real:

The two Sith Lords retired to Plagueis’s penthouse in the Kaldani Spires building to celebrate Palpatine’s upcoming success. There, Sidious plied Plagueis with wine while rehearsing the acceptance speech he would soon deliver before the Senate. Watching as Plagueis became increasingly intoxicated, Sidious waited patiently until his master fell asleep before unleashing torrent after torrent of Sith lightning upon him, basking in the Muun’s agony, as he slowly tortured his master to death.

Sometimes I wonder what goes through EU writers’ heads.