Not happy to put a bit of tarragon in the sauce (5)
I believe the answer is:
sorry
'not happy' is the definition.
I can't judge whether this defines the answer.
'put a bit of tarragon in the sauce' is the wordplay.
'put' means one lot of letters goes inside another.
'a bit of tarragon in' becomes 'rr' (I can't explain this - if you can you should give a lot more credence to this answer).
'the sauce' becomes 'soy' (soy sauce).
'rr' placed into 'soy' is 'SORRY'.
'to' is the link.
Can you help me to learn more?
(Other definitions for sorry that I've seen before include "Rueful" , "I beg your pardon" , "Repentant" , "Showing regret" , "Feeling penitent" .)