Brains holding new record over puzzle (7)
I believe the answer is:
nonplus
'puzzle' is the definition.
(I know that puzzle can be written as nonplus)
'brains holding new record over' is the wordplay.
I cannot really understand how this works, but
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is found in the answer.
'over' could be 'on' (physically on top of) and 'on' is present in the answer.
The remaining letters 'plus' 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 nonplus that I've seen before include "Flummox" , "Utterly confuse" , "disadvantageous or neutral, presumably" , "Floor" , "Throw into confusion" .)