Farro Salad with Roasted Root Vegetables

Name: Farro Salad with Roasted Root Vegetables
Ingredients: 3 cups water; 4 1/2 teaspoons kosher salt, divided, plus more to taste; 1 1/2 cups uncooked pearled farro (about 9 1/4 ounces); 3 medium carrots, peeled and cut into 3/4-inch pieces (about 1 1/2 cups); 3 medium parsnips, peeled, cores removed and discarded, and cut into 3/4-inch pieces (about 1 1/2 cups); 1 small yellow onion, cut into 3/4-inch pieces (about 2 cups); 1 1/2 cups chopped peeled celery root (about 3/4-inch piece); 6 tablespoons extra-virgin olive oil, divided; 1/4 cup chopped fresh flat-leaf parsley, plus parsley leaves, for garnish; 3 tablespoons red wine vinegar, plus more to taste; 1/2 teaspoon black pepper, plus more to taste