I've looked for documentable recipes from this period as well; the closest thing I could find is a (very good) article which translates and discusses two early 13th century recipe collections:

Hieatt, Constance and Jones, Robin. "Two Anglo-Norman Culinary Collections Edited from British Library Manuscripts Additional 32085 and Royal 12.C.xii". Speculum, Volume 61, Issue 4 (Oct. 1986), pp 859-882.

This article is available on JSTOR, if you happen to have access to it via college, etc. If you don't, you could probably get photocopies interlibrary loan, or if all else fails contact me privately and I'll mail you a copy!

If YOU happen upon anything earlier, please let me know...