From Justice League Unlimited:
In the episode, "This Little Piggy", Circe (guest star Rachel York) had turned Wonder Woman (Susan Eisenberg) into a pig. That prompts Batman (Kevin Conroy) to recruit an old childhood crush, Zatanna (Jennifer Hale) to help.
We've already seen the Dark Knight croon Cole Porter's "Am I Blue", but earlier, Circe, posing as a cabaret singer, belts out a version of Fats Waller's "Lulu's Back in Town". It does appear as though Circe's performance has been edited, as we move right into a climatic battle between Circe and Zatanna.
It's just too bad the entire episode isn't available intact, and if you've not seen it on CW, time's running out, as the Vortexx block will be discontinued in September.
Ya know, there are still some fans who think they could've furthered the prospect of Batman & Zatanna as a couple, instead of Batman & Wonder Woman, and I'm in that camp.