For the bacon and onion cake, knead flour, butter, water and salt. Let rest in the refrigerator for 30 minutes. Cut the onion and bacon into strips.
Fry the bacon in oil, add onion and fry until translucent. Season with pepper. Whisk the creme fraiche with the eggs and salt.
Roll out the dough and place it in a tart pan. Spread the onion and bacon on top. Pour the egg mixture on top. Bake in the oven for about 35 minutes.