Heat 1 tablespoon of the oil in a large pan, add the mushrooms and cook over a high heat for 5 minutes, stirring all the while to ensure they don't catch. Remove from the pan and set aside.
Add the remaining oil to the pan and cook the onions, potatoes and thyme over a medium-low heat for 10 minutes until tender and just beginning to turn golden.
Pour in the stock and milk and return the mushrooms to the pan. Bring to a gentle simmer and cook for 10 minutes, or until the potatoes are tender and cooked through.
Remove the thyme sprigs from the pan and discard. Use a hand blender to purée the soup until smooth. Season with freshly ground black pepper to taste.
To serve, ladle into warm bowl, swirl in a drizzle of the cream and scatter over the pine nuts and parsley.
Cook's tip: you don't need to chop the vegetables too neatly because the soup is blended at the end. For an extra special touch, use a mix of wild mushrooms.