Sober tea-user seen blotto (7)

I believe the answer is:

austere

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

'sober' is the definition.
(I've seen this in another clue)

'tea-user seen blotto' is the wordplay.
'tea-user' can be anagrammed to 'AUSTERE'.
However, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for austere that I've seen before include "Severe, lacking comforts" , "Hard" , "severely self-disciplined" , "Severe in manner" , "Stern, severe" .)

I've seen this clue in The Sun.

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