Clean, wash and slice the zucchini. Peel and wash the potatoes and cut or slice them thinly. Clean, wash and halve tomatoes
Grate cheese. Mix eggs, cream, sour cream and 1/3 cheese. Season with salt, pepper and nutmeg
Put the zucchini, potatoes and 2/3 of the tomatoes in a greased casserole dish. Pour egg cream over it. Sprinkle with rest of cheese
Bake gratin in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C / gas: level 3) for 45-50 minutes. Wash the parsley and remove the leaves. Garnish gratin with the remaining tomatoes and parsley
You can freeze this gratin after baking and cooling (shelf life 2-3 months). Later thawed in a hot oven at 200 °C for only about 20 minutes