Tries purchasing marrow with pudding (3,1,2)
I believe the answer is:
has a go
'tries' is the definition.
(I've seen this in another clue)
'purchasing marrow with pudding' is the wordplay.
I cannot quite see how this works, but
'pudding' could be 'sago' (I've seen this before) and 'sago' is present in the answer.
The remaining letters 'ha' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for has a go that I've seen before include "Attempts to stop a criminal" , "Confronts criminal" , "In modern jargon, makes an effort, gives it a shot" .)