New ginger nuts extremely brittle, with an indefinable quality (5-7)

I believe the answer is:

genre-busting

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'an indefinable quality' is the definition.
The definition suggests a singular noun which matches the answer.

'new ginger nuts extremely brittle' is the wordplay.
'new' indicates an anagram.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'brittle' with its centre removed is 'be'.
'ginger'+'nuts'+'be'='gingernutsbe'
'gingernutsbe' with letters rearranged gives 'GENRE-BUSTING'.

'with' is the link.

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