Pudding with a drop of rum in elaborate feast (6)
I believe the answer is:
afters
'pudding' is the definition.
(both can mean dessert)
'drop of rum in elaborate feast' is the wordplay.
'drop of' says to take the initial letters (the smallest possible amount of the word).
'in' means one lot of letters goes inside another.
'elaborate' indicates an anagram (an elaborate version of the letters).
The first letter of 'rum' is 'r'.
'feast' with letters rearranged gives 'aftes'.
'r' going within 'aftes' is 'AFTERS'.
'with a' acts as a link.
(Other definitions for afters that I've seen before include "Dessert (colloq.)" , "Dessert, sweet" , "Strafe with desserts" , "Informal desserts, puddings" , "food for pudding" .)