Katharine McPhee took on a tall order: Florence + the Machine! The 'Smash' star covers 'Shake It Out' on an upcoming episode of the NBC hit.

In the episode, McPhee's character, Karen, takes on some side singing gigs to make rent. When she gets booked at a bar mitzvah, she performs the 'Ceremonials' hit. McPhee chatted with AOL Music about the decision behind the performance.

"Believe it or not, when I was told I was going to sing with a bar mitzvah band, I thought, 'What could we do?'" the 'American Idol' alum said. "Of course everyone thought it should be an old standard but the label and I put our heads together to think what might be very cool and also fun."

McPhee's sweet voice seems more suited to her usual Broadway-style fare, though it may be because Florence Welch's vocals are incredibly distinct -- no one on the planet can really emulate her (though Katy Perry did a pretty good spoof). In any case, she does a solid job tackling the track -- and she loved every minute of it!

"We went through a bunch of songs and when I heard this last year, I knew we had to do it," McPhee gushed. "Florence + the Machine's record had not come out yet but we had heard the song and thought this would be amazing especially in this setting. So far this is one of my favorites."

Listen to Katharine McPhee Cover 'Shake It Out' (Florence + the Machine Cover)