Then USA manipulated butter producer (4,3)

I believe the answer is:

shea nut

'butter producer' is the definition.
(shea nuts contain shea butter)

'then usa manipulated' is the wordplay.
'manipulated' indicates anagramming the letters.
'then'+'usa'='thenusa'
'thenusa' is an anagram of 'SHEA-NUT'.

(Another definition for shea nut that I've seen is " West African source of butter".)

I've seen this clue in The Independent.

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