Butter, again half of it goes on one fruit (8)
I believe the answer is:
rambutan
'one fruit' is the definition.
(rambutan is a kind of fruit)
'butter again half of it goes on' is the wordplay.
'butter' becomes 'ram' (I've seen this before).
'again' becomes 'anew' (synonyms).
'half of' indicates taking half.
'it' becomes 'but' (I can't explain this - if you can you should give a lot more credence to this answer).
'goes on' is a charade indicator (letters next to each other).
'anew' with half the letters taken is 'an'.
'an' put after 'but' is 'butan'.
'ram'+'butan'='RAMBUTAN'
Can you help me to learn more?
(Another definition for rambutan that I've seen is " Bright red Malaysian fruit".)