Frenchman let recipe defrost (4)
I believe the answer is:
melt
'defrost' is the definition.
(I know that defrost is a more specific form of the action melt)
'frenchman let recipe' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'recipe' indicates an anagram.
'let' is an anagram of 'elt'.
'm'+'elt'='MELT'
(Other definitions for melt that I've seen before include "Turn to liquid" , "Liquefy with heat" , "Reduce from a solid to a liquid state" , "Become liquefied" , "Liquefy; become tender" .)