What can be bittersweet: having nothing left with lots to go round? (8)
I believe the answer is:
molasses
'what can be bittersweet having nothing' is the definition.
I can't tell whether this definition defines the answer.
'left with lots to go round?' is the wordplay.
'left with' becomes 'ol' (I can't justify this - if you can you should believe this answer much more).
'lots' becomes 'masses' ('mass' can be a synonym of 'lot').
'to go round?' means one lot of letters goes inside another.
'ol' put within 'masses' is 'MOLASSES'.
Can you help me to learn more?
(Other definitions for molasses that I've seen before include "Syrup drained from raw sugar for some lass" , "Thick treacle left over after refining raw sugar" , "US name for treacle" , "Dark syrup extracted from sugar cane" , "Thick syrup extracted from sugar cane" .)