When filling cobblers, cook in the oven (5)
I believe the answer is:
roast
'cook in the oven' is the definition.
(I've seen this before)
'when filling cobblers' is the wordplay.
'when' becomes 'as'.
'filling' means one lot of letters goes inside another.
'cobblers' becomes 'rot' (I've seen this before).
'as' placed within 'rot' is 'ROAST'.
(Other definitions for roast that I've seen before include "& 3 Accompaniment to Yorkshire pudding?" , "Heat strongly - criticise excessively" , "Cook in closed oven" , "Cooked joint" , "Oven joint" .)