Pie does improve instalment (7)
I believe the answer is:
episode
'instalment' is the definition.
(synonyms)
'pie does improve' is the wordplay.
'improve' is an anagram indicator.
'pie'+'does'='piedoes'
'piedoes' with letters rearranged gives 'EPISODE'.
(Other definitions for episode that I've seen before include "Incident in a story or part of a serial" , "Instalment of broadcast serial" , "Incident or event as part of sequence" , "One of a related series of events" , "One programme of a series" .)