Horneburger Pfannkucher - N Germany Apple of the Year

I was amused to see, in my Kleingarten monthly magazine, that they have named the Horneburger Pfannkucher http://pomologen-verein.de/fileadmin/user_upload/Landesgruppen/2016_Horneburger_Pfannkuchen.pdf as their Apple of the Year.  I suspect that this is what is growing in my Kleingarten because:
--The apple looks right
--The timing looks right
--The apple is indeed super sour from the tree, and it mellows a bit after storage
--It grows in very marshy ground, which much of my garden is
--My Kleingarten is indeed in the burg of Horn, which is a village that was absorbed by Hamburg

It's a lovely mature tree that I have sadly neglected for a few years.  We have not yet pruned it, and we bought the Kleingarten from an elderly couple who probably hadn't pruned it in years either.  It bears very heavily.  When they say very sour, that is an understatement.  It makes fine applesauce, and I've got a couple of boxes in storage (packed in fallen leaves).

My garden neighbor, who is full of opinions, thinks it's a terrible tree, but I'm pretty happy with it.

My terrible translation of the PDF below:
Origin:  Collected from town of Horn's Marsh Dam around 1840, discovered and developed by Altland (fruit growing region on the other side of the river Elbe) fruit grower Jakob Köpke in neighboring Neukirchen
Pick in: October
Eat in: November through March
Fruit form:  Big to very big fruit, round, often irregular, ridged around the flower
Skin:  Shiny to lightly rough, early green, later yellow with red top color
Fruit flesh: Initially hard and very sour, later milder
Tree: Very robust and strong-growing, even in wet moor-like ground, triploid which means no pollen saving?
Distribution: Earlier in the lower (northern) Elbe and the neighboring areas widely distributed, in first place in Altland statistics from 1939
Source: E. Brandt, Of Apples and Men, Fischerhude 2014
Note: Very beloved as a storable baking and sauce apple

Wow, I hope you have kept and protected that tree! There is so much biodiversity that has been lost because "what tastes sweet, sells", but when you have other plans for your apples than just eating out of hand, particularly that stores well with minimal special infrastructure, it would be a keeper in my books!

The former owners planted the apples on my land. One ripens in late July and early August and doesn't store at all. The second ripens in mid August and barely stores through mid-September - it would store a bit longer if I had a proper cold cellar, but alas, not any time soon. The third ripens late Sept early October, but the apples are very small, so not handy for cooking, when it's finally cool enough to want to cook!

What sort of things to do make with these apples when you do cook them?

I have 3 on 3 different rootstock from my friend in Leinzell DE. 1st apple tasting October, late, 2024. Giant and plainly sour,, not Sauer like Ashmeads or Belle de Boskoop or Goldrush(v. Sour). I'll be grafting this spring a few more if interested