Peel the potatoes, cut into slices and cook in a little salted water for about 10 minutes.
Peel and finely chop the onions. Clean the mushrooms and cut them in slices. Fry both in 1 tablespoon of oil in a pan. After 5 minutes add the spinach. Season to taste with salt, pepper, nutmeg, a little lemon juice and 2 tablespoons of sour cream.
Drain the potatoes in between and layer them together with the vegetables in a greased baking dish. Cut the sheep`s cheese into large pieces and add to the potato-vegetable mixture.
Bake the casserole in the preheated oven at 200 ° C on the middle rack for about 15 minutes. Serve hot.
Tip: The vegetables can also be replaced by other vegetables, just like the sheep`s cheese can also be replaced by mozzarella or Emmentaler, etc.