Peel potatoes and cut into small cubes, then boil in the soup until soft.
Fry olive oil, porcini mushrooms and thyme in a pan over high heat until well browned.
Puree the fully cooked potatoes with a blender, then stir in the sour cream or whipped cream well. If necessary, puree again so that it combines well.
After another 5 minutes, season the soup with salt and pepper and whisk.
Arrange the soup in bowls and add the roasted porcini mushrooms, serve immediately.