Heat oven to 350°F. Lightly butter a 9x13-inch baking dish with 1 tbsp of the melted butter.
Warm 1.5 cups broth until steaming. Keep the remaining 0.5 cup broth at room temperature.
Whisk condensed soup, sour cream, and 0.5 cup broth in a large bowl until smooth.
Fold in chicken, onion, celery, mixed vegetables, garlic powder, poultry seasoning, parsley, pepper, and salt.
Spread the chicken mixture evenly in the prepared baking dish.
In another bowl, combine stuffing mix with 5 tbsp melted butter. Pour over 1.5 cups hot broth and stir to moisten.
Let the stuffing rest 2 to 3 minutes, then fluff and scatter it evenly over the chicken layer.
Cover with foil and bake 20 minutes. Uncover and bake 15 minutes more until bubbly and golden.
Rest 5 minutes before serving so the filling sets.