9 across
Having
cooked
bean
soup,
one
requires
attendance
(8)
Having cooked bean soup, one requires attendance (8)
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The definition is at the end of the clue.
How the clue works
Right, so one requires attendance is your definition — a subpoena is exactly that, a legal order dragging you into court whether you like it or not. The trick's in "cooked", which tells you to anagram "bean soup" — chuck those letters in a pot and stir, and out comes SUBPOENA.