Enjoy!
For a very comprehensive site for medieval and early modern cooking, go toGuter Spise It's a site set up by the Society for Creative Anachronism, where there are some people with huge amounts of expertise in this area. It includes an annotated bibliography, several collections of recipes, and the instructions for getting onto their cooks' mailing list.
Lorenza de'Medici's various cookbooks make reference to several historical sources the earliest of which are probably Renaissance. Better libraries might carry her cookbooks but they are relatively current and popular (she has a PBS show - you may have to hunt for this). Theoretically, you should be able to find Lorenza's cookbooks a good-sized book store, then check out the bibliography for medieval information. Many of her recipes are modernized versions of historical sources, which she quotes from time to time in introductions to her recipes.
A revised edition of Pleyn Delit: Medieval Cookery for Modern Cooks (University of Toronto Press) is currently in print. Some of these recipes are a bit odd by modern standards (like onion tart with currants), but certainly informative about the medieval diet. It combines transcriptions of original recipes (mostly 15th-century) with modernized versions, quantities and temperatures.
For medieval Arabic recipes from Spain, see Lucie Bolens, c. 1994, entitled La Cocina Arabo-Andalus. There is also a book on Almohad cookery, but the exact reference was unavailable at this writing.
See Constance B. Hieatt & Robin F. Jones, Two Anglo-Norman Culinary Collections Edited from British Library MSS Additional 32085 and Royal 12.C.xii," _Speculum_ 61/4 (October, 1986), 859-92. These recipes are for a wide range of things, from something called 'oranges' made with ground pork & sprinkled with sugar, to fritters, ravioli, and 'White Saracen Broth'.
A contemporary cookbook, The Splendid Table, which deals with the cuisine of Emelia-Romagna, Lynn Rosetto Casper has many recipes that are adapted and holdovers from medieval and renaissance regional dishes, plus some fascinating history.
If you can read French, check out Laurioux, Bruno. Les livres de cuisine médiévaux (Typologie des sources du moyen age occidental, Fasc. 77; Brepols: Turnhout-Belgium, 1997). If you are planning to actually cook something, however, look for Constance B. Hieatt, Brenda Hosington, and Sharon Butler, Pleyn Delit: Medieval Cookery for Modern Cooks. 2nd ed. (Toronto: University of Toronto Press, 1996), paperback.
