Food critic scratching bottom quickly (6)
I believe the answer is:
presto
'quickly' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for presto that I've seen before include "hey......,cries the magician" , "rapidly" , "quick to score" , "Moving quickly" , "Immediately" .)