Barley and Shiitake Mushroom Risotto

Name: Barley and Shiitake Mushroom Risotto
Ingredients: 6 cups vegetable stock; 1/2 onion; 2 carrots, halved; 2 celery sticks, large chop; 2 tablespoons extra-virgin olive oil; 1 cup pearled barley; 2 tablespoons minced shallots; 2 cloves garlic, minced; 1/2 Vidalia onion, cut into 1/4-inch dice; 1 teaspoon kosher salt; 1 pound shiitake mushrooms, stemmed, thinly sliced; 3 sprigs fresh thyme, leaves stripped; 2 tablespoons unsalted butter, cubed; 3/4 cup grated Parmesan; 1/2 teaspoon fresh ground black pepper; 2 tablespoon finely chopped flat-leaf parsley