Boil the potatoes in salt water for 15 minutes. Drain the water and set them aside to cool. Grate the mozzarella cheese. Clean and smash the garlic. Spread the butter over the bottom of an oven proof dish. Mix the milk with the eggs, the garlic, and 1 tea spoon of salt, pepper according to your taste and some freshly grated nutmeg. Be careful not to add too much nutmeg. Taste the mixture before grating more nutmeg if you feel it is necessary. Peel the potatoes, cut them into slices and put them into the oven proof dish. Pour the milk-egg mixture over the potatoes and spread the grated cheese on top of it.
Bake in the oven at 200 degrees for around 15 minutes until the milk has set and the cheese has melted. Then switch to the grill until the cheese has formed a lovely golden crust and serve immediately. You can prepare this dish some time in advance and put it into the oven, once your guests arrive.