01 - Preheat oven to 350°F. Generously butter a 9x13-inch baking dish.
02 - Place potatoes in a large pot, cover with cold water, add 1 tsp salt, and bring to a boil. Simmer for 18-20 minutes until just tender. Drain, cool, and slice into 1/4-inch rounds.
03 - Place eggs in a saucepan, cover with cold water, bring to a boil, and simmer for 10 minutes. Drain, cool under cold running water, peel, and slice.
04 - Melt 1 tbsp butter in a skillet over medium heat. Sauté onion until translucent, about 5 minutes. Set aside.
05 - Arrange one-third of potato slices in the bottom of the baking dish. Season lightly with salt and pepper.
06 - Add half the egg slices, half the sausage slices, and half the sautéed onions. Spread one-third of sour cream over the layer.
07 - Add another layer of potatoes, remaining eggs, remaining sausage, remaining onions, and another third of sour cream.
08 - Finish with remaining potatoes. Season with remaining salt and pepper. Spread remaining sour cream over top. Dot with butter and sprinkle with breadcrumbs if desired.
09 - Bake for 40-45 minutes until golden and bubbly. Let stand 10 minutes before serving.