The poem is built on a pun. "Bookkeeping" suggests ledgers and accounts, and "cook the books" is the phrase for falsifying them. Here the phrase is turned literal: the "we" in the poem are cooking books as if they were food, and the result is an "over-hasty dinner."
What the speaker feels is hard to pin down, but the word "taste" comes first, so the experience is lingering and a little sour. A hurried meal is rarely satisfying, and the suggestion is that something rushed, or perhaps dishonest, has been served up. The poem doesn't say who "we" are or why the books are being cooked, so the reader has to fill in the gap. It could be a joke about shady accounting, or a comment on how we swallow reading and information too quickly without digesting it.
The mood is wry and slightly uneasy. It's playful on the surface, but the bad aftertaste stays with you.