Mix sour cream and crème fraîche in a big bowl.
Add the salt, pepper and the flour while stirring slowly.
Place the bowl with the liquid in the fridge for approx. one hour.
Crumb the yeast in a big bowl, add some water and stir it together so it is lump free. Let the yeast rest for thirty minutes.
Mix flour, salt and pepper in a bowl.
Add the water and the yeast in the flour and work it to shiny and smooth dough.
Let the dough rest in the bowl with moist towel on top in the oven. Don´t start the oven while the dough rest in it.
Take out the dough from the oven divide it in eight equal balls.
Roll the dough in very thin round bottoms. Place the bottoms on baking paper.
Cut the smoked pork, the onions, and the mushrooms in thin small pieces.
Take out the liquid from the fridge and spread it evenly on the eight bottoms.
Spread evenly the onions, smoked pork and the mushrooms on the bottoms.
Sprinkle the rapeseed oil on the tarte flambées.
Put the tarte flambée in the middle of the oven for twenty minutes.
Take out the first tarte flambée and serve it directly.
Place the second tarte flambée in the oven while eating the first one.