Crossword Genius

Hot bap topping, perhaps (2,1,4)

Ross

I believe the answer is:

on a roll

I'm a little stuck... Click here to teach me more about this clue!

'hot' is the definition.
(I've seen this in another clue)

'bap topping perhaps' is the wordplay.
I cannot quite understand how this works, but
'bap' could be 'roll' (I've seen this before) and 'roll' is located in the answer.
The remaining letters 'ona' 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 on a roll that I've seen before include "Having long spell of good luck" , "Piano music was once stored here" , "Where one may find sesame seeds" , "Where registered names are" , "enjoying continuing success" .)

I've seen this clue in The Daily Express.
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