Runza (1950)

[Barnhart]

I'm inclined not to count this an Americanism.  It comes from _beurre
roux_, meaning "brown butter," according to MW10  The reduced form of
the term, i.e. _roux_, may however be an Americanism.  Cajun roux and
Creole roux are interesting American variants.  I imagine there are
plenty of food terms which are compounds one formative element of which
is either Creole or Cajun.  There may even as in this case be both
Creole ... and Cajun ... with significant differences.

Regards,
David Barnhart