Preheat oven to 375°F and grease a 9x13 inch baking dish with cooking spray or butter.
In a large bowl, combine cooked chicken, condensed cream of chicken soup, and chicken broth; stir until well combined and creamy.
Spread the chicken mixture evenly in the prepared baking dish.
In a medium bowl, place the dry stuffing mix; drizzle melted unsalted butter over it and toss with a fork until all crumbs are coated.
Evenly sprinkle the buttered stuffing mixture over the chicken layer without pressing down.
Bake for 25 to 30 minutes, until the casserole is bubbly around the edges and the stuffing topping is golden brown and crisp.
Remove from the oven and let rest for 5 to 10 minutes before serving.