For the dough baking mix and 170 ml lukewarm water in a mixing bowl. Knead to a smooth dough with the dough hook of the mixer. Cover the dough and let it rise in a warm place for about 30 minutes.
For the topping, peel the onions and cut them into thin rings. Wash and clean the mushrooms if necessary, dab dry and cut into thin slices. Heat the oil in a pan. Fry the diced ham, onions and mushrooms for about 2 minutes. Season with salt and pepper. Mix sour cream and caraway.
Cut the dough in half, knead and roll out into oval flat cakes (approx. 20 x 30 cm each). Place on two baking trays lined with baking paper. Spread half sour cream on each and spread half of the mushroom mixture on top. Bake one after the other in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for about 15 minutes. Wash the chives, shake dry, cut into fine rolls and sprinkle over the tarte flambée.