A fantastic wine? (4)

I believe the answer is:

asti

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

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

'a fantastic' is the wordplay.
'ASTI' is hidden within the letters.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for asti that I've seen before include "town in Italy" , "Italian wine - (then change a letter for ...)" , "Italian product" , "Bubbly wine" , "- spumante, It. wine" .)

I've seen this clue in the Evening Standard.

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