Lightly rinse and drain mushrooms. Discard shiitake stems. Slice mushrooms into bite-size pieces.
In a large saucepan over medium-high heat, melt butter. Stir in shallots and cook until lightly browned, about 4 minutes. Add mushrooms and thyme. Cook, stirring often, until mushrooms are lightly browned, 8 to 10 minutes. Add sherry and broth; cook, stirring, until soup boils. Cover and simmer to blend flavors, 2 to 3 minutes. Season with salt and pepper.
Divide soup among 4 serving bowls and top each with a few fresh thyme sprigs or parsley leaves.
*If using shiitakes, discard stems.
Note: Nutritional analysis is per serving.