Nice woman prepared sandwiches before midday (6)
I believe the answer is:
madame
'nice woman' is the definition.
('woman' in French, eg in Nice)
'prepared sandwiches before midday' is the wordplay.
'prepared' becomes 'made' ('make' can be a synonym of 'prepare').
'sandwiches' means one lot of letters goes inside another (to sandwich is to block something in).
'before midday' becomes 'am'.
'made' enclosing 'am' is 'MADAME'.
(Other definitions for madame that I've seen before include "Book by Flaubert" , "Proprietress of a brothel" , "Flaubert novel" , "French Mrs" , "Married woman abroad" .)