1Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish with butter.
2Mix cooked chicken, sour cream, onion, cream of chicken soup, and milk in a large bowl; pour into the prepared baking dish.
3Bake in the preheated oven until hot, about 15 minutes.
4Stir 1/2 cup Cheddar cheese into the mixture and arrange unbaked biscuits over top of casserole. Sprinkle remaining 1/2 cup Cheddar cheese over biscuits.
5Return to oven and bake until biscuits are done in the middle and the chicken mixture is bubbling, 25 to 30 more minutes.
Footnotes
Tip
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.