Directions

1. Pour 2 cups boiling water over 2 cups dried porcini mushrooms in a heatproof bowl. Let stand for 20 minutes. Drain the mushrooms in a colander over a bowl, reserving the mushroom broth; set the mushrooms aside. Strain the mushroom broth through a cheesecloth-lined colander into a bowl; discard the solids. Add 3 tablespoons cornstarch, 1¾ teaspoons salt, 1½ teaspoons pepper, 1½ teaspoons dried thyme, ½ teaspoon dried tarragon and the remaining 1 cup boiling water to the mushroom broth; stir to combine.
2. Heat 2 tablespoons oil in a medium nonstick skillet over medium-high heat. Add 2 cups shallots and 2 tablespoons garlic; cook, stirring occasionally, until the shallots are soft, 4 to 5 minutes. Add ⅔ cup sherry; bring to a boil and cook for 30 seconds. Remove from the heat.
3. Stir the porcini mushrooms, broth mixture, shallot mixture and 3 pounds sliced fresh mushrooms together in a 5-quart slow cooker. Cover and cook on High until the vegetables are very tender and the flavors blend, about 4 hours. Transfer 2 cups of the soup to a blender. Remove the centerpiece of the blender lid (to allow steam to escape); secure the lid on the blender. Place a clean towel over the opening in the blender lid (to avoid splatters). Blend until smooth, about 10 seconds (use caution when blending hot liquids). Return the pureed soup to the slow cooker. Cook, uncovered, on High until slightly thickened, about 10 minutes. Gently stir in 1½ cups cream. Ladle the soup into bowls. Garnish with fresh thyme leaves and ground pepper, if desired.