Peel the potatoes and cut them into ½ finger thick slices. Transfer the potatoes to a pan, add the milk, oregano to taste, the nutmeg, the salt and, over low heat, mix it all together.
Boil the potatoes and turn off the heat once they've cooked through.
Add the cheese, and mix it all together until dissolved.
Transfer it all to a glass baking dish, gently arrange the potatoes to keep them from breaking down and cover them with grated mozzarella.
Bake in a preheated oven at 200°C (392°F) until the cheese melts.