As a bit of a disclaimer, I'll start off with a note that the editor of the books mentioned below was kind enough to send me a copy of each. Had he not done so I probably wouldn't have mentioned them, mostly for two reasons: first because I generally don't read historical fiction, and second because I have a lousy memory.
Many many months ago I received an email asking for details about a particular medieval recipe. This happens fairly often, and I try to give as useful an answer as time allows. In this particular case the author was interested in including a few recipes with her most recent book, and was asking about one recipe in particular - Towres. In a brief email exchange, I helped make sense of the Middle English and work out what type of recipe and such, and then promptly forgot about the whole thing.
As it turned out, Barbara Reichmuth Geisler's third book (a prequel) in The Averillian Chronicles includes a few authentic medieval recipes at the end. That combined with the positive reviews of her two earlier books is enough to catch my attention. In spite of my predisposition to Science Fiction and Fantasy, these books are now in my "To Read" stack (that's the short stack, as opposed to my "To Read Someday" stack, which is much bigger).