Sauce served up on a primarily unappetising dish (5)
I believe the answer is:
pilau
'dish' is the definition.
(pilau is a kind of dish)
'sauce served up on a primarily unappetising' is the wordplay.
'sauce' becomes 'lip' (I've seen this before**).
'served up' shows that the letters should be reversed in order.
'on' is a charade indicator (letters next to each other).
'primarily' suggests taking the first letters.
The first letter of 'unappetising' is 'u'.
'lip' backwards is 'pil'.
'pil'+'a'+'u'='PILAU'
(Other definitions for pilau that I've seen before include "Oriental rice dish" , "Spiced rice dish" , "Indian dish of rice boiled with meat, vegetables, spices etc" , "Speciality" , "Type of rice" .)