Put the baking mix and 170 ml of lukewarm water into a mixing bowl. Knead to a smooth dough with the dough hook of the hand mixer. Cover the dough and let it rise in a warm place for about 30 minutes.
Peel onions and cut thin rings. Wash and clean the mushrooms, dab dry and cut into thin slices. Cut bacon into strips. Heat oil in a pan. Fry bacon, onions and mushrooms for about 2 minutes.
Season with salt and pepper. Mix crème fraîche and caraway. Halve the dough, knead and roll out into oval flat cakes (approx. 30 x 20 cm Ø). Place on 2 baking trays lined with baking paper.
Spread half of the crème fraîche on a dough oval and spread half of the mushroom mixture on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 15 minutes.
Cover and bake the flat cakes as well. Wash the chives, shake dry and cut into fine rolls. Sprinkle the chives over the tarte flambée.