Put the flour in a bowl and press a depression in the middle. Crumble the yeast and stir with the sugar until liquid. Add 7 tablespoons of lukewarm water and stir. Pour into the hollow, mix with some flour from the rim and sprinkle.
Cover and leave to rise in a warm place for 10-15 minutes. In the meantime peel and halve the onions and cut them into half rings. Dice the bacon and drain in a hot pan. Add onions and stir-fry for 2-3 minutes.
Season with a little salt and pepper and let it cool down. Add oil and 1/2 teaspoon of salt to the pre-dough on the flour rim. Knead everything to a smooth yeast dough. Cover the dough and let it rise for 20-30 minutes.
Mix sour cream, egg yolk and some salt, pepper and nutmeg. Roll out the yeast dough thinly on a greased and floured baking tray (approx. 32 x 39 cm). Spread icing on the dough and sprinkle with bacon and onions.
Bake in the preheated oven (electric range: 225 °C/ convection oven: 200 °C/ gas: level 4) for 12-15 minutes on the lower rack. Cut into pieces and serve immediately.