Peel the potatoes and dice them.
Put the potatoes in a pot full of water to boil until they are tender if pierced with a fork.
Slightly butter the mould on all sides.
Drain the water from the pan, add the butter, cover with a lid for 2 minutes, till the butter is melted.
Mash the potatoes until they are soft.
Mix the ricotta, eggs and half the grated cheese. Season with salt and pepper.
Distribute the potato mixture in the square mould. Sprinkle the remaining cheese over with a little nutmeg.
Bake at 180 °C for 45-50 minutes, until the top is slightly swollen and golden brown.
Remove from the oven and leave to rest for 15 to 20 minutes before serving.