Use a knife on some stuff in a cup (3,2)
I believe the answer is:
cut up
'cup' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Maybe you can see an association between them that I can't see?
'use a knife on some stuff' is the wordplay.
I cannot really understand how this works, but
'stuff' could be 'cu' (Cu is an example) and 'cu' is located in the answer.
The remaining letters 'tup' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'in a' is the link.
Can you help me to learn more?
(Other definitions for cut up that I've seen before include "Abrupt change; pace" , "Destroy with scissors" , "Distressed - dissected" , "Very unhappy" , "Sliced; distressed" .)