Top up and serve half of rich smorgasbord (9)
I believe the answer is:
potpourri
'smorgasbord' is the definition.
(thesaurus)
'top up and serve half of rich' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'and' is a charade indicator (letters next to each other).
'serve' becomes 'pour' (**).
'half of' indicates taking half.
'top' in reverse letter order is 'pot'.
'rich' cut in half is 'ri'.
'pot'+'pour'+'ri'='POTPOURRI'
(Other definitions for potpourri that I've seen before include "Pleasant-smelling mixture" , "Mixture of dried, scented items" , "assortment of botanical stuff?" , "Flower petals and spices used as perfume" , "Fragrant mixture" .)