Crossword Genius

Perhaps Tom’s finished the sauce (6)

Ross

I believe the answer is:

catsup

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

'sauce' is the definition.
(I know this)

'perhaps tom's finished the' is the wordplay.
I cannot really see how this works, but
'tom's' could be 'cats' and 'cats' is located in the answer.
'finished' could be 'up' (eg 'time's up' means the time is finished) and 'up' is found in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for catsup that I've seen before include "Relish" , "something saucy from US" .)

I've seen this clue in The Independent.
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