Squeeze the sausage mixture out of the skin and place in a hot pan, fry well, turning constantly.
Peel the apples, cut into rings and remove the core.
Melt the butter in a saucepan, add the apples and sauté briefly.
Peel the boiled potatoes and cut into cubes. Peel and finely chop the onion. Put both in the fried fat and fry.
Layer the potatoes, apples and sausage mixture one after the other in a baking dish.
Whisk eggs and milk, season with salt and paprika and pour over the layered ingredients. Put the pie on the lowest rack in the oven and bake for about 30 minutes.