Old English coc, from Vulgar Latin cocus "cook," from Latin coquus, from coquere "to cook, prepare food, ripen, digest, turn over in the mind" from PIE root *pekw- "to cook" (cf. Oscan popina "kitchen," Sanskrit pakvah "cooked," Greek peptein, Lithuanian kepti "to bake, roast," Old Church Slavonic pecenu "roasted," Welsh poeth "cooked, baked, hot"). Germanic languages had no one native term for all types of cooking, and borrowed the Latin word (Old Saxon kok, Old High German choh, German Koch, Swedish kock).
There is the proverb, the more cooks the worse potage. [Gascoigne, 1575]
late 14c., from cook (n.); the figurative sense of "to manipulate, falsify, doctor" is from 1630s. Related: Cooked, cooking. To cook with gas is 1930s jive talk.
To tamper with and falsify records, esp financial accounts: The managers had cooked the books to the tune of $34 million/ He's been cooking the books for so many of those companies (1940s+)