Peel and finely chop the onion. Clean the mushrooms and chop finely. Chop walnut kernels coarsely. Heat 20 g fat in a frying pan, fry the mushrooms and half of the onion cubes in it while turning until they start to brown. Season the mushrooms with salt, pepper and nutmeg, put them in a bowl and let them cool down a little
Pre-cook the pasta in plenty of boiling salted water for 5-6 minutes. Drain the pasta onto a sieve, place in a bowl and cover with cold water. Leave the noodles in it for about 5 minutes
Stir cream cheese and walnuts into the warm mushroom mixture. Drain the pasta well on kitchen paper and fill with the mushroom mixture. Place in a wide, flat casserole dish. Pour in approx. 3/8 litres of hot broth. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 25 minutes
Heat 20 g fat in a small pot. Fry the remaining onion cubes in it. Add flour and sauté briefly while stirring. Add milk and 1/8 litre stock, bring to the boil while stirring and add frozen spinach. Cover and simmer for 5-6 minutes. Stir from time to time until the spinach is defrosted. Season sauce with salt, pepper and nutmeg
Spread the spinach cream sauce on 4 plates. Arrange the drained pasta on top