Of a very high standard, 'boron' clued cryptically (6,4)
I believe the answer is:
cordon bleu
'of a very high standard' is the definition.
'boron clued cryptically' is the wordplay.
'cryptically' indicates anagramming the letters.
'boron'+'clued'='boronclued'
'boronclued' with letters rearranged gives 'CORDON BLEU'.
(Other definitions for cordon bleu that I've seen before include "(Of cookery) very high standard" , "Of the highest culinary order" , "Highest class (cooking)" , "distinguished chef" , "High class chef" .)