Contents of menu binder covered by German improvements (12)
I believe the answer is:
enhancements
'improvements' is the definition.
(I know this)
'contents of menu binder covered by german' is the wordplay.
'contents of' indicates the central letters (the letters on the inside of the word).
'binder' becomes 'cement' (I've seen this before).
'covered by' means one lot of letters goes inside another.
'german' becomes 'Hans' (common German name).
The central letters of 'menu' are 'en'.
'cement' going within 'hans' is 'hancements'.
'en'+'hancements'='ENHANCEMENTS'
(Another definition for enhancements that I've seen is " Improvements".)