Scorch the surface of (4)
I believe the answer is:
sear
'scorch the surface of' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sear that I've seen before include "Scorch, brand" , "Dried-up, parched" , "Burn briefly" , "Cauterize" , "Cauterise" .)