Roll out the puff pastry and let it thaw on a baking sheet. Preheat the oven to 200 ° C top / bottom heat.
Heat the forest mushrooms with a little vegetable oil in a large pan and let the resulting mushroom water boil down completely. Stir in the Provence herbs, then add the onions and apples to the pan and sauté for 5 minutes. Season to taste with salt and pepper.
Spread the puff pastry with the sour cream and distribute the contents of the pan on top. Bake for 30 minutes, then remove from the oven and let cool down briefly.