In a pot over medium heat, brown the mushrooms and onion in the butter. Continue cooking until the mushrooms are caramelized and the juices have completely evaporated. Add the broth, potatoes and dried mushrooms. Bring to a boil.
Cover and simmer about 20 minutes or until the potatoes are tender.
In a blender, purée the soup until smooth. Return to the saucepan. Season with salt and pepper. Keep warm.
In a large non-stick skillet over medium heat, brown the porcini mushrooms in the butter. Add the remaining mushrooms and cook until they have softened. Season with salt and pepper.
Pour the mushroom soup into bowls. Top with the sautéed mushrooms. Garnish with the fresh herbs.
Note from Ricardo
Try local wild mushrooms in this recipe. Otherwise, use a mix of farmed mushrooms (shiitake, oyster, portobello, etc.) available in most grocery stores.