Way to extract essence, taking two months (6)
I believe the answer is:
decoct
'way to extract essence' is the definition.
(to decoct something is to extract its essence)
'two months' is the wordplay.
'two months' means two substitutions for 'month'.
'month' becomes 'dec' (abbreviation for December).
'month' becomes 'oct' (abbreviation for October).
'dec'+'oct'='DECOCT'
'taking' acts as a link.
(Other definitions for decoct that I've seen before include "herbal extract" , "Extract essence from (archaic)" , "extract by boiling" .)