Put the flour in a bowl and press a depression in the middle. Crumble the yeast and dissolve with the sugar in 150 millilitres of lukewarm water. Pour into the hollow and mix with some flour from the edge and sprinkle. Cover and leave to rise in a warm place for ten to 15 minutes. Meanwhile peel and dice the onions.
Dice bacon as well and fry in a pan. Add the onions and stir-fry for two to three 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 to 30 minutes. For the icing, mix quark, crème fraîche, egg yolk and some salt, pepper and nutmeg. Roll out the yeast dough thinly on a greased and floured baking tray (approx. 32x39 cm). Spread icing on the dough and sprinkle with bacon and onions. Bake in the preheated oven (electric cooker: 250 ° C/ gas: level 5) for twelve to 15 minutes.
Cover the dough and let it rise for 20 to 30 minutes. For the icing, mix quark, crème fraîche, egg yolk and some salt, pepper and nutmeg. Roll out the yeast dough thinly on a greased and floured baking tray (approx. 32x39 cm). Spread icing on the dough and sprinkle with bacon and onions. Bake in the preheated oven (electric cooker: 250 ° C/ gas: level 5) for twelve to 15 minutes. Cut the finished Flammenkuchen into large pieces and serve warm. Makes twelve pieces