Chicken Shepherds Pie with Kale Mash

Name: Chicken Shepherd's Pie with Kale Mash
Ingredients: 1 pound Yukon Gold potatoes, peeled and chopped; 1 pound celery root, peeled and chopped; 2 cups milk; Kosher salt and freshly ground pepper; 3 cups chopped kale (about 2 ounces); 1 bunch scallions (white and light green parts only), chopped; 6 tablespoons unsalted butter; 2 large shallots; 3 carrots, chopped; 2 tablespoons all-purpose flour; 1 cup low-sodium chicken broth; 1 1/2 pounds skinless, boneless chicken thighs, cut into 1/2-inch pieces; 1/4 cup chopped fresh chives; 1/4 cup chopped fresh parsley