Tenner spent on cheese ingredient (6)
I believe the answer is:
rennet
'cheese ingredient' is the definition.
(curdled milk used in cheese)
'tenner spent' is the wordplay.
'spent' indicates an anagram.
'tenner' with letters rearranged gives 'RENNET'.
'on' is the link.
(Other definitions for rennet that I've seen before include "Cheese-maker's substance" , "Curdler of milk" , "cheesy setter?" , "Milk curdling agent" , "what you need to make cheese" .)