Bruno Mars and Esperanza Spalding take us straight back to the '40s on "Old & Crazy."

It's no secret that Bruno Mars' musical stylings have always had a taste for the retro (please see: "Locked Out Of Heaven"), but we never thought he'd go all out and release "Old & Crazy," a jingly-jangly, might-as-well-have-been-released-in-the-'40s-style, boogie-woogie banger. But he did, and we dig it.

Listen to Bruno Mars's "Old & Crazy" featuring Esperanza Spalding after the jump.

Slated as the bonus track on Unorthodox Jukebox's Target Deluxe Edition, Bruno enlisted the help of last year's Grammy Award winner for Best New Artist, Esperanza Spalding. A playful and kitschy track, both the "Young Girls" singer and Esperanza take turns cooing about the crap that goes along with getting old: "Will you still call me ‘baby’ when I’m old and crazy?" While we can understand why this tune was relegated to "bonus track" status (it's not exactly a sexified pop single), it's simple, sweet, and definitely worth a listen. Even better, blast it while you're wearing an apron and cooking a rump roast for dinner and apple pie for dessert!  It'll enhance the effect.

+ Listen to Bruno Mars's "Old & Crazy" featuring Esperanza Spalding.

Photo credit: Atlantic Records