Mix flour, sugar and 1/2 teaspoon salt in a bowl. Warm milk lukewarm, crumble yeast into it and dissolve it while stirring. Add milk and yeast mixture and butter to the flour mixture. Knead to a smooth dough with the dough hooks of the hand mixer. Cover the dough and let it rise in a warm place for about 40 minutes
In the meantime peel and halve the onions and cut them into fine strips. Clean and wash spring onions and cut into fine rings. Finely dice the bacon and leave it out in a pot. Add oil, heat up, fry onions and spring onions for about 15 minutes while turning. Remove from the stove
Knead the dough once again on a floured work surface with floured hands. Roll out to a circle (approx. 33 cm Ø) on a floured work surface. Grease a springform pan (26 cm Ø) and dust with flour. Put the dough into it, pressing the rim slightly. Let it rise again in a warm place for about 30 minutes
Stir the sour cream and eggs together. Season vigorously with salt, pepper and nutmeg. Sprinkle the base with breadcrumbs. Press the base flat again, spread the onion mixture on top, pull the edge up again if necessary and pour the egg glaze over it. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) on the lower rack for 50-60 minutes, cover with aluminium foil if necessary. Remove from the oven and leave to rest on a cake rack for about 10 minutes. Remove from the springform pan, cut into pieces and arrange
waiting time 30 minutes