End in French harbour after granny ate fish (6,7)
I believe the answer is:
finnan haddock
'fish' is the definition.
(finnan haddock is a kind of fish)
'end in french harbour after granny ate' is the wordplay.
'end in french' becomes 'fin' ('end' in French).
'harbour' becomes 'dock' (I've seen this before**).
'after' says to put letters next to each other.
'granny' becomes 'nan'.
'ate' becomes 'had' (e.g. I had an ice cream).
'nan'+'had'='nanhad'
'dock' after 'nanhad' is 'nanhaddock'.
'fin'+'nanhaddock'='FINNAN HADDOCK'
(Other definitions for finnan haddock that I've seen before include "Type of cured fish" , "Smoked fish (from Kincardineshire?)" .)