Warm the milk and 1 tablespoon of sugar lukewarm. Crumble yeast into it and dissolve. Mix flour and 1 tsp. salt. Add 3 tablespoons of oil and yeast milk. Knead everything smooth. Cover and leave to rise in a warm place for at least 45 minutes.
Onions peel and roughly chop. Clean, wash and cut the spring onions into rings. Dice bacon.
Heat 2 tablespoons of oil in a large frying pan or a wide saucepan. Fry the bacon in it until crispy, take it out. Fry diced onions in frying fat for 15-20 minutes until translucent. Add spring onions and fry briefly.
Let the onions cool down.
Knead the dough again. Roll out on a greased fat pan (approx. 32 x 39 cm). Press the rim up about 1 cm. Spread onions and 2⁄3 bacon on top. Let it rise again for about 20 minutes.
Whisk the eggs and sour cream, season with salt and pepper and spread over the onions. Bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for 25-30 minutes. Wash the chives and cut into rings.
Take out the cake. Sprinkle with chives and rest of bacon. Serve warm.