You'll Be Mine

From Wikipedia:

“You’ll Be Mine” is a short song, composed by Lennon–McCartney in the Beatles’ early years. It was a humorous parody of the Ink Spots. It consists of Paul McCartney singing in a deep baritone, offset with shrill falsetto backing vocals, and guitar strumming. The lead vocal sings, in rather confused lyrics, about his determination of making a woman his; while the falsettos wail the last word of each sentence. About halfway through the song, John Lennon gives a mock-bass voice spoken interlude about how, when the woman brought him toast one morning, he looked into her eyes and saw a “National Health Eyeball“, then proceeded to love her like he has never done before. The song rises to a crescendo of wailing and bellowing, then fades out in laughter. To add to the confusion, the song is very difficult to understand; clicks, buzzes, fuzz, giggling, and the baritone voice obscure the lyrics.

Recorded in the McCartney family bathroom in 1960, it is the earliest song attributed to the Lennon–McCartney songwriting partnership to be officially released. Along with the other songs recorded on that day, it is one of the few known Beatles recordings to feature Stuart Sutcliffe on bass. Lennon’s spoken section provides insight into his love of wordplay.

From Anthology 1 liner notes:

You’ll Be Mine is a fun number, performed in a manner reminiscent of the Ink Spots, the popular American singing combo. Paul sings the lead vocal and delivers a rousing finale, and John adds a memorably outlandish spoken middle section that embraced the Beatles’ collective love for the absurd and, with the phrase “National Health eyeball“, his own fondness for word-play.

Officially appears on

Bootlegs

Live performances

Paul McCartney has never played this song in concert.