Flavouring with sandwiches makes sense (7)
I believe the answer is:
aniseed
'flavouring' is the definition.
(I've seen this before)
'with sandwiches makes sense' is the wordplay.
'with' becomes 'and'.
'sandwiches' indicates putting letters inside (goes on either side like a sandwich).
'makes sense' becomes 'i see' (I've seen this in another clue).
'and' going around 'isee' is 'ANISEED'.
(Other definitions for aniseed that I've seen before include "Cake flavouring" , "Liquorice-flavoured seeds" , "Aromatic flavouring" , "Strong herbal flavouring" , "Strong flavouring often used in sweets" .)