Soup du jour? Its trimmings sustain First Lady on run (9)
I believe the answer is:
developer
'soup' is the definition.
(thesaurus)
'du jour? its trimmings sustain first lady on run' is the wordplay.
I cannot quite understand how this works, but
'lady' could be 'eve' (I've seen this before) and 'eve' is located in the answer.
'run' could be 'lope' (lope is a kind of run) and 'lope' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for developer that I've seen before include "solution for picture-maker" , "It creates image" , "Photographic reagent" , "Property magnate" , "Film-treating fluid" .)