What does the cryptic crossword clue "Cook chard in bun and mollusc (10)" mean?

The wordplay uses an anagram. anagram of CHARD + IN + BUN = NUDIBRANCH The answer is NUDIBRANCH.

Cook chard in bun and mollusc (10)

Daily Mail Cryptic #16472 | 13 Down | 2020-12-21 flower