In a 3-quart saucepan cook and stir leek, celery, and garlic in hot butter until tender. Add mushrooms; cook and stir about 5 minutes more or until mushrooms are tender. Stir in undrained tomatoes, broth, whipping cream, dillweed, and pepper. Bring to boiling; reduce heat. Simmer, covered, for 30 minutes.

Let soup cool slightly. Transfer soup mixture, half at a time, to blender or food processor. Cover and blend or process until smooth. (Or use an immersion blender.) Return all of the soup mixture to saucepan; heat through. To serve, ladle soup into bowls. If desired, top each serving with additional mushrooms. Makes 4 side-dish servings.

Note: If using shiitake mushrooms, remove and discard tough stems before slicing.