Tart fixed with better filling (8)

I believe the answer is:

strumpet

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

'fixed with better filling' is the wordplay.
'fixed with' becomes 'set' (both can mean decided or determined. I am not sure about the 'with' bit.).
'better' becomes 'trump' (both can mean to outdo or beat).
'filling' means one lot of letters goes inside another.
'set' placed around 'trump' is 'STRUMPET'.

Can you help me to learn more?

(Other definitions for strumpet that I've seen before include "Hussy" , "Prostitute" , "... unlike her!" , "'... City' (novel by James Plunkett)" , "call girl" .)

I've seen this clue in The Sunday Times and The Times.

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