Send up note for producer of junket (6)
I believe the answer is:
rennet
'producer of junket' is the definition.
(junket is made from curdled milk or rennet)
'send up note' is the wordplay.
'send up' is a reversal indicator.
'note' becomes 'tenner' (a ten pound sterling bank note).
'tenner' in reverse letter order is 'RENNET'.
'for' is the link.
(Other definitions for rennet that I've seen before include "Cheese curdling agent" , "Causing vomiting" , "Cheese-making curdler" , "It's used to curdle milk for cheese" , "cheese maker?" .)