Exciting soap, perhaps, for best-seller? (3,4)

I believe the answer is:

hot cake

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'for best-seller?' is the definition.
I can't tell whether this definition defines the answer.

'exciting soap' is the wordplay.
'exciting' becomes 'hot' (similar in meaning).
'soap' becomes 'cake' (I can't explain this - if you can you should give a lot more credence to this answer).
'hot'+'cake'='HOT CAKE'

'perhaps' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

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