Barley Risotto with Roasted Winter Vegetables

Name: Barley Risotto with Roasted Winter Vegetables
Ingredients: 4 cups chicken or vegetable broth, homemade or low-sodium canned; 2 sprigs fresh thyme; 1 medium carrot, sliced; 1 small celery root (about 1/2 pound), peeled and cut into 3/4-inch chunks; 1/2 small butternut squash, halved, peeled, seeded, and cut into 3/4-inch chunks; 4 tablespoons extra-virgin olive oil; 1 teaspoon kosher salt, plus additional for seasoning; 1 cup pearl barley; 1/2 medium onion, chopped; 2 cloves garlic, smashed; 1/2 cup dry white wine; 4 to 5 cups torn mustard greens (1 small bunch); Freshly ground black pepper; 1 cup freshly grated Parmesan, optional