Small, well-known Austrian bread product (6)
I believe the answer is:
sarnie
'bread product' is the definition.
(informal term for a sandwich)
'small well-known austrian' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'well-known austrian' becomes 'Arnie' (Arnold Schwarzenegger).
's'+'arnie'='SARNIE'
(Other definitions for sarnie that I've seen before include "Popular bread-based snack (colloq)" , "Sandwich (slang)" , "Sandwich (informal)" , "no classy fare" , "Two slices of bread with a filling" .)