Cook with spices that existed back then (5)

I believe the answer is:

devil

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'cook with spices that' is the definition.
'devil' can be an answer for 'cook' (thesaurus). I am not certain of the rest of the definition.

'existed back then' is the wordplay.
'back' indicates one should take the final letters (the letter at the back).
'then' becomes 'evil' (I can't explain this - if you can you should believe this answer much more).
The last letter of 'existed' is 'd'.
'd'+'evil'='DEVIL'

Can you help me to learn more?

(Other definitions for devil that I've seen before include "Unsurpassed" , "Imp" , "Powerful evil spirit" , "Fiend" , "Demon" .)

I've seen this clue in the Sydney Morning Herald.

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