Clean and wash the spinach. Peel and finely chop the onion. Heat oil in a pan and fry the onion in it. Add the spinach dripping wet and let it collapse. Season with salt, pepper and nutmeg.
Fill spinach, noodles, herring fillets with sauce into a greased casserole dish. Mix cream and 400 ml water and stir in the bag contents. Bring to the boil while stirring and pour over the casserole. Sprinkle the cheese over it and bake in a preheated oven (electric: 200 °C/ gas: level 3) for approx. 25 minutes. Serve garnished with dill as desired