Preheat & Prep: First, get your oven ready by preheating it to a cozy 400 degrees Fahrenheit (200°C). Then, lightly grease a 9x13 inch baking dish; cooking spray is perfect for this.
Sauté the Veggies: In a medium skillet, melt the butter over medium heat. Add your diced onion and sliced celery, stirring until they become beautifully soft and translucent, usually about 5-7 minutes. This step adds a lovely depth of flavor!
Layer the Chicken: Spread the shredded chicken evenly across the bottom of your prepared baking dish. Next, sprinkle the cooked onion and celery over the chicken.
Create the Creamy Sauce: In a separate small bowl, whisk together the condensed cream of chicken soup and milk until the mixture is smooth. Gently pour this creamy sauce evenly over the chicken and vegetables in the baking dish.
Add the Stuffing: Sprinkle the dry chicken stuffing mix in an even layer over the creamy chicken mixture.
Pour the Broth: Carefully pour the chicken broth over the stuffing layer, making sure it's distributed evenly so the stuffing can absorb it.
Bake to Perfection: Cover your baking dish tightly with aluminum foil. Place it in the preheated oven and bake for 25 minutes.
Serve Warm: Remove the casserole from the oven. Let it rest for a few minutes before serving this incredibly easy and comforting meal warm!