Dissolve crumbled yeast in 60 ml lukewarm water and milk. Stir in 1 teaspoon of flour. Cover the yeast pre-dough and let it rise for about 10 minutes. Put the rest of the flour in a bowl. Add oil and 1/2 teaspoon of salt and stir gently.
Stir in the yeast predough and work into a smooth dough with the dough hooks of the hand mixer. Cover and leave to rise in a warm place for about 30 minutes. In the meantime, sift the spinach, wash thoroughly and drain.
Peel and finely chop the onion. Melt the fat in a pot and fry the onion until transparent. Add spinach and let it collapse. Season with salt, pepper and nutmeg. Put the spinach in a colander and drain.
Express additionally. Grate cheese finely. Stir sour cream, eggs, cheese (up to 2 tablespoons) and semolina until smooth. Season to taste. Grease a springform pan (24 cm Ø). Roll out 2/3 of the dough on a floured work surface in springform pan size.
Line the floor with it. Form the remaining dough into a roll, place it on the edge of the springform pan and press it up to a rim with your fingers. Add the spinach. Pour over the vegetables. Clean and wash the tomatoes and press them into the mixture.
Sprinkle with remaining cheese. Bake in the preheated oven (electric cooker: 200 °C/ gas: level 3) for about 1 hour. Results in about 12 pieces.