3/4 pound shiitake, stems discarded, caps sliced 1/4 inch thick
1 garlic clove, thinly sliced
Kosher salt and freshly ground pepper
1 tablespoon unsalted butter
1/2 cup freshly grated Parmigiano-Reggiano cheese
In a medium pot of salted boiling water, cook the barley for 15 minutes. Drain the barley and let it cool slightly. In a medium saucepan, bring the chicken stock to a boil; reduce the heat to low and keep warm.
In a large saucepan, heat the olive oil. Add the mushrooms and garlic and season with salt and pepper. Cook over moderately high heat, stirring, until the mushrooms are softened and the garlic is fragrant, about 4 minutes. Add the barley and stir to coat. Add 1 cup of the warm stock and cook over moderately low heat, stirring constantly, until nearly absorbed. Continue adding the stock 1 cup at a time, stirring constantly between additions, until the barley is al dente and suspended in a creamy sauce, about 25 minutes. Stir in the butter and cheese. Season with salt and pepper and serve.