Shepherds Pie with Celery Root Puree

Name: Shepherd's Pie with Celery Root Puree
Ingredients: 2 pounds celery root (2 to 3), peeled and cut into 2-inch chunks; 3 cups chicken broth; Kosher salt and freshly ground black pepper; 2 tablespoons extra-virgin olive oil; 1 large yellow onion, diced; 2 medium carrots, peeled and cut into 1/4-inch dice; 1 stalk celery, cut into 1/4-inch dice; 2 cloves garlic, chopped; 1 teaspoon fresh thyme leaves; 1 pound ground dark-meat turkey; 3 tablespoons all-purpose flour; 2 tablespoons unsalted butter; 2 cups frozen peas, defrosted