In a big stock pot over medium heat pour the olive oil. When the oil is hot, add the shallots thinly sliced and let them cook.
Add the brown mushrooms and wait until they are soft (about 3 minutes), then add the white mushrooms and the garlic and let it soften too for a couple minutes.
Pour the chicken broth and wait until boil.
Dissolve the cornstarch in the milk and make sure that there are no lumps.
Pour the milk and add a pinch of salt and white pepper and let it simmer for 5 minutes until it starts to get thicker.
Pour the soup into the blender and blend for a minute in high speed.
Serve with some butter croutons and enjoy! (note 1)