cook除了“烹饪”，还有“捏造”或“篡改”的意思；book不仅指“书”，还指“账本”，所以，cook the books是指“做假账”、“隐瞒真实的利润和开支”。

【例句】
Rank amateurs who know nothing about how to cook the books.
这是完全不懂做假帐的业余会计的水平。

My boss was caught by the police recently, because he secretly cooked the books and moved a big sum of money to his private account.
我老板最近被警察抓走了，因为他虚报账目，而且把一大笔钱存到了自己名下。