Sauté the mushrooms for a few minutes in the olive oil. Remove a few for garnish, then add the onion and chopped garlic, and cook for about 10 minutes.
Add the chicken or vegetable stock and 1tbsp fresh thyme and simmer for 25 minutes. Season well and add a handful of chopped parsley and a dash of cream.
Purée with a stick blender - add a dash more water if the soup is too thick.
Serve with a drizzle of extra virgin olive oil or truffle oil, the reserved mushrooms, freshly ground black pepper and crusty bread.