Wash the potatoes and cook covered for about 20 minutes. Clean the spinach and wash or defrost it. Peel and finely dice onion and garlic
Fry the onion and garlic in hot oil until transparent. Add the spinach and let it collapse. Season to taste with salt, pepper and nutmeg. Pour into a flat ovenproof dish
Quench and peel the potatoes. Wash the tomatoes. Cut the potatoes, tomatoes and mozzarella into thin slices and spread on the spinach
Bake everything in the preheated oven (electric cooker: 200 °C/recirculating air: 175 °C/gas: level 3) for 10-15 minutes