For the tarte flambée, prepare the puff pastry according to the instructions and place on a baking tray lined with baking paper. Preheat the oven to 200 °C. Spread crème fraîche evenly on the dough.
Peel, press or finely chop garlic and spread evenly as well. Cut leek and onion into fine rings, also spread on the dough and season with salt and pepper. Sprinkle bacon cubes and mountain cheese on top. Bake the tarte flambée for about 20 minutes and serve hot, sprinkled with oregano and garnished with basil.