6 cups vegetable or mushroom broth (low sodium)
½ cup water
2 tablespoons extra-virgin olive oil
1 small onion, minced
2 cloves garlic, minced
3 cups shiitake mushrooms, coarsely chopped
1½ cups pearl barley, rinsed
½ cup white wine
1/3 cup freshly grated Parmesan cheese
1 tablespoon butter
Freshly ground pepper, to taste
Bring broth and water to a simmer in a large saucepan. Adjust heat to maintain a steady simmer.
Heat oil in a large Dutch oven over medium-high heat. Add onion and garlic and cook, stirring, until the onion is translucent, about 2 minutes. Add mushrooms and cook, stirring, until they begin to release their juices, 2 to 3 minutes.
Add barley and cook, stirring, for 1 minute. Add wine and simmer, stirring, until most of the liquid has evaporated, about 1 minute more. Reduce heat to medium.
Add ½ cup hot broth to the barley and cook, stirring, until most of the liquid has been absorbed. Continue adding ½ cup hot broth at a time and stirring until the liquid has been absorbed after each addition, adjusting the heat to maintain a gentle simmer, until the barley is tender and creamy but still somewhat firm, 35 to 45 minutes. (You might not use all the broth.)
Remove from heat. Stir in cheese and butter. Season with pepper.