Boozer with extremely impressive belly button (5)

I believe the answer is:

innie

'belly button' is the definition.
(informal term for a concave navel)

'boozer with extremely impressive' is the wordplay.
'boozer' becomes 'inn'.
'with' means one lot of letters go next to another.
'extremely' means to remove the middle letters.
'impressive' with its centre removed is 'ie'.
'inn'+'ie'='INNIE'

I've seen this clue in The Guardian.

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