Long, impressive recipe starts off backwards (4)

I believe the answer is:

epic

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'long impressive' is the definition.
'epic' can be an answer for 'impressive' (epic can mean grand or impressive). I'm unsure of the 'long' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for epic that I've seen before include "blockbuster" , "Long narrative poem telling of a hero's deeds" , "Exodus, say" , "Vast in scale" , "Tale of heroic deeds" .)

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

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