Melt the butter. Heat the sour cream and dissolve the yeast in it. Knead the prepared ingredients with flour and 1/2 teaspoon salt to form a dough and cover in the refrigerator for 30 minutes.
Quarter the mushrooms and fry in 2 - 3 tablespoons of olive oil, season with salt and pepper. Remove the mushrooms from the pan. Cut the zucchini into slices and sauté in the oil for about 5 minutes, season with salt and pepper. Halve the tomatoes.
Roll out the dough (diameter approx. 34 cm). Grease a quiche pan and line it with the batter. Spread the vegetables on top. Mix the cream with the eggs and season. Finely chop the marjoram and thyme and stir in.
Pour the cream mixture over the vegetables and bake in a preheated oven at 175 ° C for 40 - 45 minutes. Grate the cheese and sprinkle over the vegetable cake 20 minutes before the end of the cooking time.