Sheath cake?

Does anyone know the origin of the phrase "sheath cake"?
I assume it is just a mispronounciation of "sheet cake," but I have had several conversations with people who are insistent that although the pan is called a sheet pan, the cake is a sheath cake.

Barry Popik says that “sheet cake” is older, and “sheath cake” possibly came into use because "'sheet' sounds like a word that cannot be printed here”.
Are the people who tell you it's “sheath cake” from Texas, by any chance?

Why, yes, in fact, they are from Texas! I currently live in Texas but did not grow up here, so some of the colloquialisms are beyond me.

says that “sheet cake†is older, and “sheath cake†possibly came into use because “'sheet' sounds like a word that cannot be printed hereâ€.
And sheath cake doesn't?
You can say "shit" here as long as it's in a discussion of language and not an epithet hurled.