Cut the peeled potatoes into slices or chunks and put them to boil in salted water with a little butter. Preheat some butter separately and fry the flour. Dilute it with the milk while stirring and add salt to taste. Once cooled down, beat the eggs with the sauce and dilute the sauce with a little of the broth from the potatoes.
Pour the half boiled potatoes in a greased pot with the chopped onions and pour in the sauce that you have already mixed with the grated cheese. Sprinkle with a little rosemary and put it to bake for about 20 minutes or until deliciously browned.