Pie filling (7)
I believe the answer is:
custard
'pie filling' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for custard that I've seen before include "Egg/milk bake" , "Sweet sauce made with milk and eggs" , "Yellow sauce" , "-- Pie; -- apple" , "Pudding accompaniment" .)