Pastry is a new filling food (6)
I believe the answer is:
danish
'pastry' is the definition.
(I've seen this in another clue)
'a new filling food' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'filling' is an insertion indicator.
'food' becomes 'dish' (dish is a kind of food).
'a'+'n'='an'
'an' inserted inside 'dish' is 'DANISH'.
'is' acts as a link.
(Other definitions for danish that I've seen before include "Like Hamlet or bacon?" , "Copenhagen this capital" , "course includes article / noun combination" , "Word linking blue and pastry" , "European language" .)