Preheat oven 375 degrees. Grease 9x13 casserole dish with cookie spray and set aside.
In a large mixing bowl, combine hash browns, ranch dressing, buffalo sauce, soup and 1 cup cheddar cheese and mix well. Cube chicken and mix well.
Dump casserole ingredients into casserole dish, cover with foil and bake for 1 hours. Uncover and add remaining cheese on top. Bake for an additional 15 minutes until melted and bubbly. Garnish with chopped chives if desired.
Allow to cool slightly before cutting.
Keep in an air tight container in the refrigerator up to a week or in the freezer for up to two months.