Lark fails but it's an elaborate story! (8)

I believe the answer is:

fabulist

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

'an elaborate story' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'lark fails but' is the wordplay.
'fails but' anagrams to 'FABULIST'.
Though, I am not clear how the anagram is indicated.

'it's' is the link.

Can you help me to learn more?

I've seen this clue in the Irish Times.

Want a hint initially instead of a full solution? Install my app