Boil and peel the potatoes the day before, cover and chill. Soak the morels in 150 ml of lukewarm water for 1 hour. Finely dice the onions. Rinse the morels again in the sieve under running water, squeeze them out lightly and cut them roughly. Let the morel water run through a sieve lined with kitchen paper and remove the sand.
Heat 20 g butter in a small saucepan and fry 1/3 of the onions in it until translucent. Add morel water and 150 ml cream and boil down creamy and thick for 20-25 minutes over medium heat. Add the morels for the last 5 minutes. Season to taste with salt and pepper. Let cool down.
Blanch the spinach in boiling salted water, rinse and drain. Squeeze out well and chop roughly. Press the potatoes through a press into a large bowl. Season with salt, pepper and nutmeg. Add cornstarch and 2 egg yolks and work into a smooth dough. Shape into a roll on a floured work surface, divide into 4 equal pieces and shape into flat cakes. Press a deep depression in the middle and add 1-1.5 tablespoon. Add morel filling and 1 egg yolk. Carefully shape into dumplings and let simmer uncovered in slightly simmering salt water for about 20 minutes.
Roast the almonds in a pan without fat. Heat the remaining butter in a saucepan and sauté the remaining onions until translucent. Add the spinach and the rest of the cream and cook over a medium heat for 4-5 minutes. Season with salt, pepper and nutmeg. Carefully lift the dumplings out of the water with a slotted spoon, drain and serve with the spinach. Sprinkle the almonds on top and serve immediately.