Cauliflower Soup with Shiitakes

Cauliflower puree soup is surprisingly creamy, and shiitake with meat adds piquancy to the texture.
Preheat a large saucepan over high heat. Add 2 teaspoons of oil to the skillet; stir to coat. Add the leeks; saute for 1 minute. Add 1/8 teaspoon of salt. Cover, reduce the heat to low, and cook for 5 minutes or until the leeks are tender, stirring occasionally. Add the cauliflower, 1 cup and 6 tablespoons broth, 3/4 cup water, and thyme. Bring to a boil; cover, reduce heat, and simmer 7 minutes or until the cauliflower is very soft. Combine the cauliflower mixture in a blender. Remove the center part of the blender lid (to release steam); secure the blender lid to the blender. Cover the hole in the blender lid with a clean towel (to avoid splashing). Whisk until smooth. Return to the pan. Add the remaining 1/4 teaspoon salt, milk, butter, and pepper. Keep warm.Mushroom caps cut into thin slices. Preheat a large skillet over medium-high heat. Add the remaining 2 teaspoons of oil to the pan and stir to coat. Add the mushrooms; simmer for 6 minutes or until lightly browned. Add the remaining 2 tablespoons of stock, Worcestershire sauce, and sherry vinegar. Cook for 1 minute or until the liquid is reduced and syrupy.Pour about 1 cup of soup into each of the 4 bowls. Sprinkle each serving with about 2 tablespoons of the mushroom mixture. Sprinkle evenly with parsley.