Boil the potatoes in their skins in salted water - being careful not to overcook them.
Once cooled, peel and slice into rounds about 1 cm thick, and salt lightly.
In an oven-safe dish, the one you'll serve it in, layer: a layer of potatoes, then a layer of sliced hard-boiled egg - with sausage or ham slices, if using.
Keep layering until the ingredients are used up, finishing with potatoes on top.
Sprinkle the top with breadcrumbs, and scatter the butter cubes over it.
Pour the sour cream generously over the top, so it covers well.
Bake in a preheated oven at 200°C for 25-30 minutes, until the top turns golden brown.
Serve hot.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.