Put flour and salt in a mixing bowl. Make a small depression in the middle. Crumble yeast into it, sprinkle sugar over it. Warm up the milk. Add 3 tablespoons of it to the yeast and stir a little.
Cover and leave to rise in a warm place for about 15 minutes until the pre-dough has doubled. In the meantime, peel onions and cut or slice them into fine rings. Dice bacon finely and fry in a pot.
Add onions and sauté briefly. Add caraway seeds. Drain bacon-onion mixture on a sieve and let it cool down. Grease a large flat springform pan (approx. 32 cm Ø) or a baking tray.
Lightly mix the yeast dough. Add the rest of the milk and fat and work everything thoroughly with the dough hooks of the hand mixer until the dough throws bubbles and comes away from the bowl rim. Roll out on a lightly floured work surface in springform pan size.
Lay out the prepared mould with it. Press the dough firmly to the edge of the mould. Cover and leave to rise in a warm place for another 15 minutes. Grate cheese finely. Whisk sour cream and eggs. Season to taste with salt and pepper.
Spread the onion-bacon mixture on the dough. Add egg-cream and sprinkle with cheese. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for 60-70 minutes. Served warm, the onion cake is particularly delicious.
Results in about 20 pieces.