First, spend a small fortune eating in back-of-the beyond tiny towns in Catalunya or the Languedoc. (And remember that potatoes and tomatoes weren’t on the inn’s menu 900 years ago.)
Dig for some details on specific regional cuisine and its history. This can take some time, because — if you are a writer or terminally curious — you’ll wander off to find details about who was in charge of Girona at the start of the 13th C., while trying to remember details about the great food you had for lunch when you got lost in Girona.
Try to find where researchers (and likely, their beleaguered grad students) have been researching or reviving actual species that grew in Spain and the Languedoc before modern genetics made everything Better, Bigger, and Disease Resistant. For example, start with this article on Neglected Horticultural Crops by F. Nuez and J.E. Hernández Bermejo (though it dates from 1492).
Seek some medieval recipes, documented from actual cookery records, but not from England or northern France. I suggest using “bibliography” in your search string, and be prepared for half the links to have died an ignoble Internet death. And watch out for Renaissance or other later-period info — the “how to” information might be useful, but it also might have anachronisms to avoid.
Here are some example sources:
Medieval Cookbooks – An Annotated Bibliography
A Cookery Bibliography
Now, figure it out in your own kitchen—even though you likely don’t have a brick-and-plaster oven in the backyard or an open-hearth wood-fire in your kitchen.
Start with something like Catalan Cuisine by Colman Andrews — especially if you need the text to be in English. Make sure the text includes a prehistoric-to-the present background. Andrews, for example describes Guifré le Pilós (Winfred the Shaggy) and his four bloody fingers dragging over a golden shield, held by Charles the Bald, to create the first Barcelona heraldry.
Exclude what you can’t find locally or don’t have patience to try. For example, I skip any recipe that involves a whole animal, unless it’s a chicken. For roast suckling pig, I wait until my local favorite spot, Harvest Vine, is serving it.
Here’s our simple Christmas Eve medieval Languedoc menu:
Roast pork with cinnamon, pepper, prune and olive sauce*
Espinacas picadas (as enjoyed by Pèire Leteric*** in Bone-mend and Salt)
Dates, almonds, and cheeses (imported, whatever you can get through the silly cheese laws)
* You don’t have to go do all the work of Internet search-and-fail investigations to invent this. Modify the Chicken Marbella recipe from the Silver Platter cookbook.
**OK, I haven’t tried this recipe, because I don’t eat bread, but you too can have great success baking a no-knead bread in your dutch oven using the New York Times recipe.
*** From Chapter 8, “Crucesignati at Supper”:
Pèire’s favorites were foods he’d brought home from the Outre-mer and taught his farmers to grow: dried peaches stewed and softened to accompany the trout, chickpeas ground into a garlicky paste and spooned onto unleavened bread, and cracked semolina berries floating in oil with mint and onion.
And palm-dates, the only food Pèire paid good silver for, buying them right off the ships at the Narbonne docks. They tasted like burnt sugar, so chewy they required hot wine to wash away the sticky remains.