Boffin's rum -- escort necks it (twice) (6,9)
I believe the answer is:
rocket scientist
'boffin's' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for rocket scientist that I've seen before include "Clever chap" , "Mastermind" , "boffin" , "I launch farreaching studies" , "brain" .)