Cook some rhubarb or tripe (12)
I believe the answer is:
fiddlesticks
'tripe' is the definition.
(I've seen this before)
'cook some rhubarb' is the wordplay.
'cook' becomes 'fiddle' (I've seen this before).
'some rhubarb' becomes 'sticks' (I am not sure about this - if you are sure you should believe this answer much more).
'fiddle'+'sticks'='FIDDLESTICKS'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for fiddlesticks that I've seen before include "tripe" , "Bilge" , "Bother!" , "Blast!" , "Violin bows - rubbish!" .)