Crossword Genius

My muck sends off courteous setter (8,8,2)

Ross

I believe the answer is:

goodness gracious me

'my' is the definition.
(both are expressions of surprise)

'muck sends off courteous setter' is the wordplay.
'muck' becomes 'goo' (both can mean something sticky).
'off' indicates anagramming the letters.
'courteous' becomes 'gracious' (synonyms).
'setter' becomes 'me' (the setter of the clue).
'sends' with letters rearranged gives 'dness'.
'goo'+'dness'+'gracious'+'me'='GOODNESS GRACIOUS ME'

I've seen this clue in The Guardian.
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