01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish with a small amount of butter.
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 ¼-inch rounds.
03 - Place eggs in a saucepan, cover with cold water, and bring to a boil. Simmer for 10 minutes. Drain, cool under cold water, peel, and slice.
04 - Melt 1 tbsp butter in a skillet and sauté the onion until translucent. Set aside.
05 - Layer one-third of potato slices on bottom of 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, sausage, onions, and another third of sour cream.
08 - Finish with remaining potatoes, season with remaining salt and pepper, spread remaining sour cream on top, and dot with butter. Sprinkle with breadcrumbs if desired.
09 - Bake for 40-45 minutes until golden and bubbling. Let stand 10 minutes before serving.