As the book first appears in Oblivion, it's heavily implied that the "kitchen" was the Cheydinhal Dark Brotherhood sanctuary.
The details given in the book don't quite match up with the in-game design, but the key points do: three large rooms, red tinting, and the bas relief (which is a depiction of a sort of mother -- the Night Mother, a large knife in one hand and one of her children flailing in her arms while the rest watch in terror).
Considering that one sanctuary resident, Vicente Valtieri, was a vampire, the "mystery meat" was a meal of human flesh. And everyone knows that Bretons are excellent cooks...