Sieve the flour into a large bowl, press a depression in the middle. Crumble the yeast into it and mix a pre-dough with 3-4 tbsp. milk and 1 tsp. sugar. Dust with flour from the edge and let it rise covered in a warm place for about 15 minutes
Mix the remaining milk, 40 g sugar, fat in flakes, 1 egg and 1 pinch of salt into the pre-dough, knead the dough thoroughly. Cover the dough and let it rise again for about 1/2 hour
In the meantime peel the onions and cut them into thin rings. Heat 1 tablespoon of oil in portions in a large frying pan. Sauté the onions and bacon in it for about 5 minutes. Season to taste with salt and pepper. Mix sour cream, 3 eggs and starch. Season with salt and pepper
Grease a baking tray (25,5 x 40,5 cm) and dust lightly with flour. Roll out the yeast dough evenly in the tin and press to the edge with your hands. Spread the onion mixture evenly on top. Sprinkle caraway over it. Pour the sour cream and egg icing over it Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 30-35 minutes. Remove, cut into pieces and serve immediately
Waiting time approx. 15 minutes