I'll put back into cup a golden soup (12)
I believe the answer is:
mulligatawny
'soup' is the definition.
(mulligatawny is a kind of soup)
'i'll put back into cup a golden' is the wordplay.
'put back' says the letters should be written backwards.
'into' means one lot of letters goes inside another.
'cup' becomes 'mug' (I've seen this before).
'golden' becomes 'tawny' (I've seen this before).
'ill' reversed gives 'lli'.
'lli' inserted within 'mug' is 'mullig'.
'mullig'+'a'+'tawny'='MULLIGATAWNY'
(Other definitions for mulligatawny that I've seen before include "Indian soup" , "Curried soup" , "One type of soup" , "Curry flavoured soup" , "Spicy meat soup, originally from India" .)