1. Clean the mushrooms with a damp cloth and chop them roughly, leave a few for garnishing.

2. Heat the olive oil and butter in the Dutch oven or soup pot over medium heat.

3. Once the butter has melted, add the chopped onion and minced garlic. Sauté them until they become translucent.

4. Add the chopped mushrooms and teaspoon of thyme to the pot. Stir well and let them cook until they soften, for about 10 minutes.

5. Pour in the vegetable stock, bring the mixture to a boil, then simmer for 30 minutes.

6. Remove from heat and allow to cool slightly.

7. Blend the soup until smooth. You can use a stick blender for this or transfer the soup to a regular blender in batches.

8. Return the blended soup back to the pot, stir in the double cream, season with salt and pepper to taste. Heat the soup gently, but do not boil.

9. Ladle the soup into bowls, garnish with the reserved mushrooms and freshly chopped parsley.

10. Serve the Rivendell Mushroom Bisque hot, with a slice of crusty bread on the side if desired.