Tenner wasted on cheese ingredient (6)
I believe the answer is:
rennet
'cheese ingredient' is the definition.
(curdled milk used in cheese)
'tenner wasted' is the wordplay.
'wasted' is an anagram indicator.
'tenner' anagrammed gives 'RENNET'.
'on' is the link.
(Other definitions for rennet that I've seen before include "Substance that curdles milk" , "Dairy product" , "Agent for cheesemaker" , "Curdler of milk" , "Substance used to curdle milk for cheese-making" .)