every once ___ a while

[TrickyFiction]

I've been writing "every once and a while," but my husband just told me he'd always thought it was "every once in a while." Now I'm wondering which is correct. Does anyone here know?

[scarletpeaches]

In.

A conjunction wouldn't make sense; a preposition would.

[Use Her Name]

"once in a while" is the proper phrase.