“Koke bøker” means “to cook books”. The correct way is “kokebøker” and means “cookbooks”
Interesting idiom in English: To cook the books
This means to do dishonest accounting and make it look good for auditing. Might be two sets of books or similar fuckery.
I assume that "Koke boker" means to cook books physically on a stove or in an oven. But the way you stated it I might mis-interpret it to be dishonest accounting.