Cheese from farm fair goes rotten (7,5)
I believe the answer is:
fromage frais
'cheese' is the definition.
(I know that fromage frais is a type of cheese)
'farm fair goes rotten' is the wordplay.
'rotten' indicates anagramming the letters.
'farm'+'fair'+'goes'='farmfairgoes'
'farmfairgoes' with letters rearranged gives 'FROMAGE FRAIS'.
'from' is the link.
(Other definitions for fromage frais that I've seen before include "Giraffes roam (anag) - dairy product" , "food" , "Soft fresh cheese, like thick yogurt" , "Low-fat cheese" .)