Cook the potatoes in boiling salted water for about 15 minutes. Then cut into slices and layer in a greased casserole dish. Sprinkle with parmesan. Whisk milk and egg white. Season with nutmeg and pepper.
Pour over the potatoes and bake everything for about 30 minutes in the preheated oven (electric oven: 200 °C/ gas: level 3). Serve garnished with chives.