01 - Preheat the 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 but not falling apart. 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 gently sauté the onion until translucent. Set aside.
05 - Layer one-third of the potato slices on the bottom of the baking dish. Sprinkle with a little salt and pepper.
06 - Add half of the egg slices, half of the sausage slices, and half of the sautéed onions. Dollop and gently spread one-third of the sour cream over the layer.
07 - Repeat layers with remaining potatoes, eggs, sausage, onions, and another third of the sour cream.
08 - Finish with a final layer of potatoes, season with remaining salt and pepper, and spread remaining sour cream over the top. Dot with butter. Sprinkle breadcrumbs over the top for extra crunch.
09 - Bake for 40-45 minutes until golden and bubbling. Let stand 10 minutes before serving.