For the mushroom casserole, prepare the mushrooms, wash and slice them together with the onion and sauté them briefly in some hot butter.
Cut the graham crackers into thin slices as well and soak them in milk for about 30 minutes. Beat the eggs, season with salt, pepper, nutmeg and crushed garlic cloves and mix with the mushrooms, onions, graham crackers and semolina.
Put the mixture into a greased baking dish, cover with butter flakes and bake for about 30 minutes at 200°.