Vegetable served up by inn outside Northern Ireland retreat (9)
I believe the answer is:
aubergine
'vegetable' is the definition.
(I know that aubergine is a type of solanaceous vegetable)
'inn outside northern ireland retreat' is the wordplay.
'inn' becomes 'auberge' (I've seen this before).
'outside' means one lot of letters goes inside another.
'northern ireland retreat' becomes 'in' (I can't explain this - if you can you should give a lot more credence to this answer).
'auberge' going around 'in' is 'AUBERGINE'.
'served up by' is the link.
(Other definitions for aubergine that I've seen before include "I argue, Ben, that it's a fruit" , "Purple vegetable" , "Vegetable strangely found in a burgee" , "Fruit of the eggplant" , "I agree bun could become a strange vegetable" .)