Farro Salad with Roasted Root Vegetables

Crispy roasted root vegetables like parsnips and celery root add an earthy, caramelized depth to this simple grain salad made with tender, chewy farro. Resist the urge to stir the vegetables during cooking to help them develop the most color.

• 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