Mix yeast, pinch of sugar and 5 tablespoons of lukewarm water. Put flour and salt in a bowl. Add the yeast mixture, 150-200 ml lukewarm water and oil and knead to a smooth dough with the dough hooks of the hand mixer.
Let the dough rise covered in a warm place for about 45 minutes.
Peel the onions and cut or slice them thinly. Peel carrots and cut them into long strips with a peeler. Cut bacon into pieces. Drain mozzarella balls and cut in half.
Mix crème fraîche and sour cream and season with salt and pepper.
Cut the dough in half. Roll out the first half of the dough oval on a floured work surface. Put the dough on a baking tray lined with baking paper. Spread with about half of the sour cream. Spread about half of each of the onions, carrots, mozzarella and bacon on top and bake in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: see
manufacturer) bake for about 15 minutes until golden brown. Take the tarte flambée out of the oven. In the meantime prepare the 2nd tarte flambée and bake it as well.