On the menu, it's only so high (4)

I believe the answer is:

soup

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'on the menu it's only' is the definition.
I can't judge whether this defines the answer.

'so high' is the wordplay.
'high' becomes 'up' (associated in meaning).
'so'+'up'='SOUP'

Can you help me to learn more?

(Other definitions for soup that I've seen before include "First course" , "Liquid - course" , "Eg, mulligatawny" , "Preliminary course" , "Photographic developer" .)

I've seen this clue in the Evening Standard.

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