Medieval Cuisine and Agriculture

In the article "On the Impracticality of a Cheeseburger," Waldo Jaquith writes:

Further reflection revealed that it’s quite impractical—nearly impossible—to make a cheeseburger from scratch. Tomatoes are in season in the late summer. Lettuce is in season in spring and fall. Large mammals are slaughtered in early winter. The process of making such a burger would take nearly a year, and would inherently involve omitting some core cheeseburger ingredients. It would be wildly expensive—requiring a trio of cows—and demand many acres of land. There’s just no sense in it.

A cheeseburger cannot exist outside of a highly developed, post-agrarian society. It requires a complex interaction between a handful of vendors—in all likelihood, a couple of dozen—and the ability to ship ingredients vast distances while keeping them fresh. The cheeseburger couldn’t have existed until nearly a century ago as, indeed, it did not.

So often when we think that such-and-such a food was not around in the European Middle Ages, it's because the ingredients are New World. For example, you'll sometimes hear that medieval people thought tomatoes were poisonous, which is preposterous because medieval (European) people didn't think about tomatoes at all, having never seen them (here's Melissa Snell's accurate account of tomatoes in Europe). Medieval people didn't have potatoes, peanuts, squash, green beans, turkeys, chili peppers, corn, chocolate, etc.

What Jaquith's article made me wonder, though, was what modern dishes we eat that could not have existed in the Middle Ages not because of distance between new world and old, but because the harvest times of the various ingredients were so different that one could not practically make them. Since vegetables were often pickled to preserve them, I'm imagining certain kinds of salads that we take for granted today might be impossible without wilted or pickled ingredients.

I've worked on a farm in my youth, but it was with modern planting, harvesting, and so many of the plants were New World that I really have no idea about medieval agriculture -- but I'm sure many out there do. What modern dishes were impossible or impractical in the Middle Ages?