Pickle and cheese sandwiches back in fashion (5)
I believe the answer is:
brine
'pickle' is the definition.
(I've seen this in another clue)
'cheese sandwiches back in fashion' is the wordplay.
'cheese' becomes 'brie' (Brie is an example).
'sandwiches' means one lot of letters goes inside another (to sandwich is to block something in).
'back in' says to take the final letters (the 'back' of the word).
The final letter of 'fashion' is 'n'.
'brie' placed around 'n' is 'BRINE'.
'and' acts as a link.
(Other definitions for brine that I've seen before include "preservative" , "Sea water" , "pickle" , "Seawater" , "Strong salt-water solution" .)