Oven Preheating: Initiate by preheating the oven to a temperature of 350°F (175°C).
Butter Melting: Place the unsalted butter in a 9x13-inch baking dish. Insert the dish into the preheating oven, allowing the butter to melt.
Assembly of Chicken and Vegetables: Once the butter has melted, extract the pan from the oven. Arrange the shredded chicken in an even layer atop the melted butter. Subsequently, disseminate the frozen peas and carrots over the chicken. Season the layer with kosher salt, freshly ground black pepper, and garlic powder.
Preparation of Biscuit Layer: In a separate medium-sized bowl, combine the milk with the Cheddar Bay biscuit mix. Gently pour this mixture over the chicken and vegetables, taking care not to disturb the underlying layers.
Soup and Stock Mixture: Utilizing the same bowl (now empty), whisk together the cream of chicken soup and chicken stock. Carefully pour this blend over the previously added biscuit layer, ensuring the layers remain distinct.
Baking: Place the baking dish in the preheated oven, uncovered, and bake for a duration of 45-50 minutes. Upon completion, the mixture will appear runny but will solidify into a gravy-like consistency upon resting.
Resting and Serving: Allow the dish to sit for 15 minutes post baking. This resting period is crucial for the mixture to attain the desired consistency. Serve thereafter.