Crumble the yeast and mix with sugar until the yeast becomes liquid. Put flour, 1/4 teaspoon salt, oil and 150 ml lukewarm water into a bowl. Add the mixed yeast and knead immediately to a smooth dough.
Cover the dough and let it rise in a warm place for about 30 minutes.
In the meantime peel the onion and cut it into fine strips. Dice bacon finely. Clean and wash the pumpkin and slice it into thin slices with a peeler.
Cut the yeast dough into quarters, knead the dough pieces again and roll them out on a floured work surface to a thin, oval cake (approx. 15 x 30 cm). Spread the dough evenly with crème fraîche.
Season with salt and pepper. Cover 1 flat bread half with onions and bacon, the other half with pumpkin, chutney and crumbled cheese.
Place 2 tarte flambée cakes on each baking tray lined with baking paper. Bake in the preheated oven on the lower rail (electric oven: 250 °C/ convection oven: 225 °C/ gas: see manufacturer) one after the other for approx. 10 minutes.