Brownie unavailable, but required for this competition? (4-3)

'required for this competition?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'brownie unavailable' is the wordplay.
I cannot quite understand how this works, but
'unavailable' could be 'off' and 'off' is present in the answer.
The remaining letters 'bake' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'but' is the link.

Can you help me to learn more?