My guess is that EBD wrote things down phonetically and hoped for the best when she put them in her books. We were always told at school that German was very easy in that everything was written just as it was pronounced. It may work in a classroom where everything is very carefully enunciated in Hochdeutsch, but it definitely doesn't work in the real world of regional accents and everyday speech. (I speak with feeling!) Didn't we have a similar thread about pancakes, where she'd also come up with an alternative spelling?
Anyway, it just so happens that I discovered on my last trip that a secondhand bookshop had opened in the village. I couldn't resist buying 2 antiquarian cookery books. I've looked up the 1790 printed one (the other is handwritten in something called Kurrent script), and guess what? There's a recipe for cheese soup (Käß=suppe). It's in Gothic script and I don't have time right at this moment to attempt a translation, so I've taken a quick picture. When I have a bit more time, I'll sit down and look at it properly, but if anyone else gets there before me, feel free!
Edited to add:
Ok, I ended up so intrigued, I've attempted a translation. Like English, German spelling 200 years ago differs in places from that of today, so there's a bit of guesswork gone into it and I make no guarantees that I've got it absolutely right. I haven't yet been able to find out what a "Bierling" is, I've put a post on the village's FB group in the hopes that someone there might know. (I'm also not sure what a "Seidlein" is, I think probably a liquid quantity.)
Grate a 140 grams of good Edam. Pour on a pint of meat stock and a quart of water, so that it does not become too salty. Leave it to boil as long as there are still some hard lumps in it. Put it through a sieve, add half a quart of sweet cream and a piece of butter about the size of a walnut. Let it boil again and garnish it with pieces of fried bread. A little nutmeg and ginger can also be added. The cream can be omitted and 2 egg yolks stirred in instead.
This soup can also be made on Fast Days, with just water and no stock, but then a piece of butter half the size of a hen's egg is needed.
Edited again to add that I had a reply from one of the FB Group members explaining that a "Vierling" is the equivalent of 140 grams and a Seidlein a pint.