Peel, wash and slice the potatoes. Cook the potatoes in boiling salted water for 5-10 minutes until al dente. Meanwhile clean and wash spring onion, dab dry and cut diagonally into rings.
Clean, wash and slice the zucchini lengthwise. Drain potatoes and rinse in cold water. Grease an oven dish (approx. 1.6 litres capacity). Lay potato slices side by side in 2 layers, put the rest aside.
Cover potatoes with zucchini slices and boiled ham. Sprinkle with spring onions and layer the remaining potato slices in flakes. Whisk milk and eggs, season well with salt, pepper and nutmeg.
Pour egg milk over the casserole. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 40-50 minutes.