We love Barley Mushroom soup. I found this on another site, based on a recipe by renowned chef Mark Russ Lederman. Did a bit of simplification and some adjustment based on other reviewers but I think it's close to the original!
Melt the butter in a large, heavy stockpot over medium-high heat. Add onions and sauté until softened and translucent. Add the garlic and sauté about 2 minutes more. Add the fresh mushrooms, celery, carrot, and half of the parsley, and sauté until the mushrooms are golden and the celery and carrots are beginning to soften, about 10 minutes. Stir in flour until well blended. Stir in beef broth. Stir in the barley and oregano. Add salt, and pepper to taste.
Bring mixture to a boil, stirring frequently. Reduce heat to low; simmer until the barley is tender, about 30 to 40 minutes. You can add a little more water if soup is too thick. Adjust the seasoning, add sherry if using; sprinkle with the remaining parsley before serving.