Really good cook's old bouncer retrained (6,4)
I believe the answer is:
cordon bleu
'really good cook's' is the definition.
'cordon bleu' can be an answer for 'cook's' (cordon bleu is a kind of cook). I am unsure of the 'really good' bit.
'old bouncer retrained' is the wordplay.
'retrained' indicates an anagram (train can mean to shape or direct a plant).
'old'+'bouncer'='oldbouncer'
'oldbouncer' is an anagram of 'CORDON BLEU'.
Can you help me to learn more?
(Other definitions for cordon bleu that I've seen before include "(Of cookery) very high standard" , "High class chef" , "High-class cookery" , "Old bouncer (anag)" , "Of a very high standard (food)" .)