At the end, pour in sauce quickly (6)
I believe the answer is:
presto
'quickly' is the definition.
(I've seen this before)
'at the end pour in sauce' is the wordplay.
'at the end' indicates one should take the final letters.
'in' indicates putting letters inside.
'sauce' becomes 'pesto' (pesto is a type of sauce).
The final letter of 'pour' is 'r'.
'r' inserted inside 'pesto' is 'PRESTO'.
(Other definitions for presto that I've seen before include "Hey ..., according to the magician" , "quick to score" , "fast to the maximum" , "To be played quickly" , "Hey, it's a magician's word" .)