Wash the potatoes, boil in water for 25-30 minutes. Quench, peel and let cool
In the meantime peel and chop the onions. Heat 60 g fat in a pot. Fry the onions in it until transparent. Sprinkle with flour and sauté briefly. Stir in 3/4 l water, cream and stock. Bring to the boil and simmer for about 5 minutes. Melt half the cheese in it. Season to taste with salt and pepper
Cut the potatoes and sausage into slices. Layer both in a large greased casserole dish. Pour the sauce evenly over them. Sprinkle with remaining cheese. Bake in a preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 20 minutes until golden brown