Aubrey, I suspect (based on the principle that you're designing from Germanic-language roots) that even if the grains weren't quite the same, they'd still
call it "corn", or whatever the German for that is. The question is, what (plants and/or knowledge of how to use them for food) would and wouldn't have made it through the Great Darkness? I expect any crops then ripening, and possibly even many trees, would have died---but then once light returned any seeds that hadn't been eaten in the cold darkness should still work as seeds, so long as they didn't get too cold.
In my own writing (while I haven't thought much about this) it'd be most reasonable for the food to
mostly be as it is here, since the continents on which most stories are mostly set were originally settled by people from our world, many quite probably bringing seed corn and whatnot with them ... (Which gives me an idea for a story ... but that's
way off topic for this thread

) There wouldn't be much different in the preparation than you'd find
somewhere in our world, since one of the principles of my "applied metaphysics" is that the "mundane" way is usually cheaper or otherwise better. (The one obvious exception is that, until the necessary industry for modern refrigeration developed, they'd use applied metaphysics to keep food safe and fresh when they could.)
In re real-world "equivalents": If your work becomes sufficiently popular (may God provide!), and involves food notably, you may be asked to provide recipes. I know of two examples of this (though neither is a Christian author): I've read a collection of maps and other worldbuilding data about Anne McCaffrey's Pern (
The Dragon-lover's Guide to Pern I think was the title), which included a couple of recipes, including one for "klah", their stimulant beverage brewed from the bark of a Pernese tree (I think the "recipe" included tea, coffee, and chocolate, but I'm not sure). And there's a story in Patricia Wrede's anthology
Book of Enchantments about "The Frying Pan of Doom" that includes a cooking contest and, in passing, a description of the winning entry, a barbarian's "After-Battle Triple Chocolate Cake". And then in an author's note she says that immediately after reading the story, her editor called her to demand the recipe, so she created it and it's printed (in the barbarian's "original measurements and instructions" plus a "translation for modern kitchens") in the anthology after the story. (It's become a perennial favorite in our house.)