For the dough, combine all ingredients in a bowl and knead by hand until smooth. Leave to rest for 30 minutes.
Preheat the oven to 250 °C (tap and buttom heat).
In the meantime, peel the onions and cut them into very thin slices.
Divide the dough into 4 parts and roll out each part very thinly. Brush with crème fraîche, place the onions and bacon on top and season with salt and pepper.
Bake in the oven for about 10-12 minutes, let cool briefly and enjoy with a glass of wine!