For the filling cut onion and let saute in hot oil, add the chopped mushrooms and add salt and pepper.Cut spinach a little bit and add and let saute. Now pat the paste in a spring form (24cm diameter) with high sides, work the cheese cubes in the spinache mixture and sprinkle on the dough in the form. Stir egg and cream , season with salt and pepper and pour on the spinache mixture in the springform. Let bake in the preheated oven at 220°C for 25 minutes. Let stand before serving for about 5 minutes.