Clean and finely chop the onion. Heat a bit of olive oil in a pot and sauté the onion over low heat until softened.
Add the potatoes and mushrooms, and sauté over medium heat for a couple of minutes, stirring frequently.
Pour in the vegetable broth and bring to a boil. Then cover and simmer for 20 minutes.
Meanwhile, wash and chop the parsley.
Once the vegetables are tender, remove the pot from heat. Pour in the milk and stir well.
Use an immersion blender to blend the soup until smooth. If the consistency is too thin, return the pot to the stove and simmer until it thickens to your liking.
Add the chopped parsley and season with salt and black pepper. Stir well.