Puff Pastry Chicken Pot Pie

Name: Puff Pastry Chicken Pot Pie
Prep time: 10 min
Cook time: 35 min
Total time: 45 min
Cuisine: American
Ingredients: ¼ cup flour ((35 grams)); 3 tablespoons butter; 2 cups low-sodium chicken stock (, see note 1); 1 tablespoon dried sage; 1 teaspoon salt; ¼ teaspoon black pepper (, see note 2); 2.5 cups frozen vegetable mix (, see note 3); 1.5 cups cooked chicken pieces (, diced, see note 4); ½ pound puff pastry sheet (, thawed, see note 5); 1 egg (, beaten (optional))