Step 1Heat the olive oil in a large saucepan over medium heat. Add the onion, celery and leek and saute about 5 minutes, until translucent. Add the mushrooms, garlic and thyme and continue to cook for about another 5 minutes, stirring often.
Step 2Add the Sherry and simmer until reduced to 1 tablespoon, about 5 to 7 minutes. Add the vegetable stock and bring to a boil. Simmer for 15 minutes. Season to taste with salt and pepper.
Step 3Spoon some of the soup into a blender. Put the top on the blender and cover the top with a kitchen towel. Hold the top down and puree until smooth. Finish with remaining soup, working in batches. Pour into bowls and garnish with Parmesan cheese.