Pouring out a copita with the pudding (7)

I believe the answer is:

tapioca

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'pudding' is the definition.
(tapioca pudding is a kind of pudding)

I can't explain the rest of the clue.

(Other definitions for tapioca that I've seen before include "I act OAP (anag) - edible substance made from cassava" , "Starchy dish" , "Substance from cassava used to thicken puddings" , "it thickens" , "Starch from cassava used in making puddings" .)

I've seen this clue in the Evening Standard.

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