Mix the yeast, sugar and 5 tablespoons of lukewarm water. Add the flour and a pinch of salt. Pour in 150 - 200 ml of lukewarm water and the oil and knead everything until smooth. Cover and let rise in a warm place for 45 minutes.
Peel the onions and carrots. Cut the onions into rings and the carrots into strips. Drain the mozzarella and cut in half. Mix the creme fraîche and sour cream, season with salt and pepper.
Halve the dough and roll it out on a round baking sheet lined with baking paper. Brush with half of the sour cream. Spread half of the onions, carrots, mozzarella and bacon on top.
Prepare the second tarte flambée in the same way. Bake in the oven at 225 ° C (top / bottom heat, convection: 200 ° C) for 15 minutes.