Step 1Heat the olive oil in a large heavy pot over medium-high heat. Cook the celery and carrots, stirring occasionally, until slightly softened, 5 minutes. Add the onion and cook until softened, 5 minutes more. Add the mushrooms and garlic and cook, uncovered, stirring occasionally, until lightly browned, about 5 minutes.
Step 2Add the stock, soy sauce, barley and Sherry. Reduce the heat to low, cover partially, and simmer gently for 45 minutes. Add additional water as needed. Season with salt and pepper to taste. To serve, ladle into heated soup bowls.