This pudding was finished, back in time (4)

I believe the answer is:

sago

I'm a little stuck... Click here to teach me more about this clue!

'this pudding' is the definition.
(I've seen this before)

'finished back in time' is the wordplay.
'finished' becomes 's' (I can't explain this - if you can you should believe this answer much more).
'back in time' becomes 'ago' (I've seen this in another clue).
's'+'ago'='SAGO'

'was' acts as a link.

Can you help me to learn more?

(Other definitions for sago that I've seen before include "Starchy pudding cereal" , "Edible powdery starch" , "Palm cereal" , "Starchy grain used in desserts" , "Cereal, used in pudding" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.