Broken trough follows unknown dairy product (7)
I believe the answer is:
yoghurt
'dairy product' is the definition.
(yoghurt is a kind of dairy product)
'broken trough follows unknown' is the wordplay.
'broken' indicates anagramming the letters.
'follows' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'trough' anagrammed gives 'oghurt'.
'oghurt' after 'y' is 'YOGHURT'.
(Other definitions for yoghurt that I've seen before include "Dairy produce" , "Cultured food" , "spoiled dairy product" , "Bacteria-treated milk product" , "Healthy food" .)