Grease a springform pan (24 cm Ø). Coarsely grind the walnuts. Mix rye and 100 g wheat flour, nuts and 1⁄2 TL salt in a bowl. Add 100 g butter in pieces and 1 egg. Quickly knead everything into the dough with your hands - you may still see small pieces of butter.
Roll out the dough on a floured work surface until round (approx. 30 cm Ø). Line a mould with it and pull up a small rim. Put it in a cold place.
Sort the spinach, wash and drain well. Clean the mushrooms, possibly wash and halve them. Clean, wash and cut spring onions into rings. Heat the oil in a large pan. Sauté the mushrooms in it in portions.
Finally fry the spring onions briefly. Then add the spinach and let it collapse. Put all mushrooms back into the pan and season with salt and pepper. Put everything in a sieve and let it drain.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Mix crème fraîche and 4 eggs, season with salt, pepper and nutmeg. Dice cheese. Cut ham into strips. Spread mushroom mix, ham and cheese on the dough.
Pour egg icing over it. Bake in the oven on the lower shelf for 35-40 minutes. Wash the chives, shake dry and cut into small rolls. Take mushroom cake out of the oven and arrange. Sprinkle with chives.
Crème fraîche may be enough.