Thinly slice the potatoes and boil them lightly in salted water.

Heat a small amount of oil in a frying pan and saute the onions until transparent, then remove them.

Using the same pan, fry the sausages until they develop a fragrant golden color.

Layer the boiled potatoes, onion, and sausage alternately in a gratin dish.

Mix beaten eggs, milk, salt, and pepper in a bowl, then pour it into the gratin dish.