Cook made to keep back especially grand rum (8)
I believe the answer is:
demerara
'grand rum' is the definition.
'demerara' can be an answer for 'rum' (demerara is a type of rum). I am not sure about the 'grand' bit.
'cook made to keep back especially' is the wordplay.
'cook' indicates an anagram.
'to keep' is an insertion indicator.
'back' says the letters should be written backwards.
'especially' becomes 'rare' (I can't justify this - if you can you should believe this answer much more).
'rare' in reverse letter order is 'erar'.
'made' with letters rearranged gives 'dema'.
'dema' enclosing 'erar' is 'DEMERARA'.
Can you help me to learn more?
(Other definitions for demerara that I've seen before include "Type of brown sugar" , "That's sweet!" , "sweetener" , "(Light-brown) sugar" , "Source of sweetness" .)