Snack is crumbly, but it is ace (3,7)

I believe the answer is:

tea biscuit

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'snack' is the definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'crumbly but it is ace' is the wordplay.
'crumbly' is an anagram indicator.
'it is' becomes 'itis'.
'but'+'itis'+'ace'='butitisace'
'butitisace' anagrammed gives 'TEA BISCUIT'.

'is' is the link.

Can you help me to learn more?

I've seen this clue in The Independent.

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