As to Himmel und erde recipe, it is prob not 'authentic' German recipe, but:
Boil potato chunks until tender, then mash with butter (and a pinch of nutmeg if desired).
Meanwhile for the apple element either chop apples into small chunks and put in with the potatoes to boil OR make apple sauce separately by putting apple chunks in a saucepan with a tiny bit of sugar and tablespoon of water/lemon juice, cover until turned to mush.
Mix together potato and apple mixtures.
Cut up onion very small and fry in oil with a pinch of brown sugar until fully caramelized. (We like lots of onion, so do one medium-sized per person)
Either serve immediately, topped with the onion (plus crispy bacon if you like, in which case it is excellent on its own), or put the potato mix into a buttered ovenproof dish, top liberally with onion, then reheat in a medium oven when needed (maybe cover with foil if the onion starts to get too dark).
I'd feel a bit 'done' with a plain Yorkie but I'd love it if you roasted some chunks of onion, pepper, maybe squash, possibly courgette and then cooked them in the Yorkie batter, like a toad in the hole. Some rosemary or thyme would be nice in that mix too.
Otherwise, and if they are mushroom likers, a big mushroom stuffed with garlic, breadcrumbs, cheese and roasted.