Preheat the oven to 350°F. Grease a 9x13 inch baking dish.
In a large mixing bowl, combine 3 cups cooked shredded chicken, two 10.5-ounce cans cream of chicken soup, 1 cup sour cream, ½ teaspoon garlic salt, and ¼ teaspoon black pepper.
Stir everything together until fully combined.
Spread the chicken mixture evenly into the prepared baking dish.
In a separate bowl, mix 1 sleeve crushed Ritz crackers, about 30 crackers, with ¼ cup melted unsalted butter until the crackers are evenly coated.
Sprinkle the cracker mixture evenly over the top of the chicken mixture.
Bake for 25-30 minutes, or until the top is golden brown and the casserole is bubbly.
Let stand for 5 minutes before serving.
Notes
For extra flavor, add 1 cup of shredded cheddar cheese to the chicken mixture.You can use rotisserie chicken for convenience.If the topping browns too quickly, cover with foil for the last 10 minutes of baking. Refrigerate any leftovers in an airtight container for up to 5 days.