. Cover dried mushrooms with 4 cups boiling water and let stand until they have softened, about 15 minutes. Reserve the mushrooms and pour the liquid through a cheese cloth lined strainer or a coffee filter to remove any sands or solids from the liquid. Reserve the liquid.

Heat olive oil in a large soup pot over medium heat. Reserve about ½ cup of the green onions and add the rest to the heated oil with the shallots, garlic, and thyme. Cook until softened, about 5 minutes. Remove thyme sprigs and discard. Add the reserved dried and fresh shiitake mushrooms and cook, stirring, until they have released all of their juices and most of the liquid has evaporated. Add salt, pepper, and sherry. Cook until the sherry has evaporated, about 1 minute. Sprinkle the flour over the mixture, tossing to coat.

Stir in the reserved mushroom liquid and the stock. Bring to a boil, reduce the heat, and simmer for 30 minutes.

Remove about 1 cup of the mushrooms with a slotted spoon, toss with the reserved green onions.

Process the soup in small batches in a food processor or blender until smooth. Taste and season with more salt and pepper if needed. Serve the soup hot garnished with the reserved mushrooms and green onions.