Monster, WTF? Are you indeed, truly that innocent of French?
Well... it can happen. I ain't got that much German...
[puts on lecturer jacket w/suède elbow patches, fiddles w/official Flaming Carrot bubble pipe]
French has this sort of all-purpose article, "à" which can mean anything from "to, at, with, for" or "in the style of." Damn useful when you can't think what to say next, but are sure it might be one of those. Like Spanish's
del, "au" is a combo of the article and "the." It substitutes for à+le for French masculine nouns, so we get to "au jus" meaning "with juice."
"Au jus" is not a fucking noun! Do not use "with!"
Served au jus is the proper terminology, menu writers.
And
à la means "in the style or manner of."
À la mode just means it's in style; it doesn't actually mention ice cream on your pie. I'd like to find out how the phrase came about sometime.