It looks like pastry made with potato is quite a big thing in Germany. My German skills are somewhat rusty and I’m afraid I can’t tell you more in that direction but I can tell you how I got there.
The previous step was that I asked Google to translate “potato pastry” into German and it came back with the single word, kartoffelgebäck, rather than two separate words. That intrigued me and I ran a search on the German word, which yielded a lot of results. Many of those looked like they were toward the sweet end of things (lots of sugar) but Fleisch- und Kartoffelgebäck-Rezept (meat and potato pastry recipe) is definitely on the savoury side.
Another step back: I discovered the concept of potato pastry this afternoon in the recipe book The Hairy Dieters Go Veggie (Orion, 2017). Wanting it in German was merely a whim – I think Kartoffeln (potatoes) is a delicious sounding word and one of those I still remember from GCSE German. I don’t think Si and Dave made any direct German connection but their Mushroom, Leek and Chestnut Pie (in the hearty recipes section) called for the potato pastry they explain towards the end of the book. On top of half fat to flour, you add dry mashed potato (boil, drain, allow to steam off and mash without any butter or milk but a pinch of salt). Their standard portion is 40g unsalted butter, 80g flour and 275g floury potatoes (along with 15g or so of milk and that pinch of salt). Lets call that ratios of 4:8:~28 or 1:2:7 — standard pastry with a lot of potato added in.
It was easy to whizz up in a food processor and, once the milk was added, didn’t take long to ball up. The dough is quite soft, so the final flour ratio pushed up as I rolled it out. They suggested 200g of the resulting mixture rolled to 3mm thick; I got that amount to about 5mm before it was large enough to cover my pie. Once applied to the top, trimmed and washed with a beaten egg, I still had a small ball of dough and some egg left. I rolled that flat, curled the edges up and filled the space in the middle with the rest of the egg. All got baked at 170°C in our fan oven for a little over 40 minutes.
The pie was delicious, although the pastry round the edge had bonded to the dish and I could have trimmed it a bit harder. However, the real treat was the pastry and egg. We ate it while we waited for the pie to cool (it came out a few minutes earlier) and it was melt-in-the-mouth delicious. I’ll try the pie again but I definitely want to experiment with that pastry.