Handle a bit of butter (4)
I believe the answer is:
knob
I believe this is a double definition.
'handle' is the first definition.
(I know that knob is a type of handle)
'a bit of butter' is the second definition.
(knob can mean a lump of butter)
(Other definitions for knob that I've seen before include "Turn it to open door" , "Hump" , "Handle or dial" , "Small lump (of butter?)" , "Prominent rounded hill" .)