concoct (v.)

1530s, "to digest" (a sense now obsolete), from Latin concoctus, past participle of concoquere "to digest; to boil together, prepare; to consider well," from assimilated form of com "together" (see con-) + coquere "to cook, prepare food, ripen, digest," from PIE root *pekw- "to cook, ripen."

Meaning "to prepare an edible thing, combine and prepare the elements of" is from 1670s, metaphorically extended beyond cooking to "devise, plan" by 1792. Related: Concocted; concocting.