"Once in Love with Amy" (1948). From Frank Loesser website:
"As Susan Loesser recalled, the song was actually written six years earlier when Frank Loesser, Peter Lind Hayes, Haye's wife Mary Healy, were working for the Army's Radio Productions Unit in California.
""Always an early riser, he [Loesser] would already be pounding away on a muted keyboard when Mary came downstairs at 6:00 a. m. She would bring him coffee, which he appreciated so much that he wrote a song for her: 'Once in Love with Mary.' Six years later it became Ray Bolger's show-stopper.""
Frank Loesser

The PBS documentary, "Heart & Soul, The Life and Music of Frank Loesser," is available on DVD.