Cracking thoughts to trouble such a boffin? (7)

I believe the answer is:

egghead

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'a boffin?' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for egghead that I've seen before include "Ovoid-shaped intellectual" , "Very clever person" , "Intellectual person" , "Very academic person" , "Expert" .)

I've seen this clue in The Sun.

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