Clean the porcini mushrooms thoroughly and cut them into cubes.
Finely chop the onion and dice the potatoes.
Heat 2 tbsp of butter in a large pot over medium heat.
Add the finely chopped onion and sauté until the onions are soft.
Add half of the porcini mushrooms (250 g, about 1/2 lb) and cook for about 5-7 minutes until they turn lightly golden.
Pour in the white wine and let it simmer for a couple of minutes until it evaporates.
Add a few sprigs of thyme and the diced potatoes, and stir.
Pour the vegetable or mushroom broth into the pot.
Bring the soup to a boil, then let it simmer for about 15 minutes, or until the potatoes are tender.
Remove the thyme sprigs from the pot.
Use an immersion blender (or regular blender) to blend the soup until it’s completely smooth and creamy.
Add the heavy cream and stir gently. Season with salt and pepper to taste. Let the soup heat through for a couple of minutes.
Heat 1 tbsp of butter in a pan.
Sauté the remaining porcini mushrooms with fresh thyme until they are golden and crispy. Season with salt and pepper.
Pour the soup into bowls and top with the butter-fried mushrooms.
Serve with freshly baked bread and optionally an extra sprinkle of thyme.