Sort the spinach, wash thoroughly and drain. Clean, wash and thinly slice the parsley root. Wash, clean and slice the mushrooms. Peel onion and garlic.
Dice onion, press garlic through a garlic press. Heat 10 g fat in a pot, fry parsley root and garlic in it and add 1/8 litre water. Cover and simmer for about 5 minutes.
Add the spinach, cover and cook until the spinach has collapsed. Season with salt, pepper and nutmeg. Heat 20 g fat in a frying pan. Sauté the mushrooms and onions while turning and season with salt and pepper.
Heat the remaining fat in a pot and sauté the flour in it. Deglaze with stock and milk, bring to the boil while stirring and simmer for about 5 minutes. Stir in half of the parmesan and season with salt, pepper and nutmeg.
Put some sauce in a greased, ovenproof dish and cover with 3 white lasagne sheets. Spread spinach on top and pour some sauce over it. Place green lasagne sheets on top and spread mushrooms on top.
Cover with white lasagne sheets and cover with the rest of the sauce. Sprinkle with remaining parmesan and bake in the preheated oven (electric: 200°C/ gas: level 3) for 50-60 minutes.