Preheat oven to 350 degrees F. Spray a 9x13-inch baking dish with cooking spray and set aside.
In a large bowl, toss together cooked and diced potatoes, pimentos, parsley, and cheese. Spread in prepared baking dish.
Pour melted butter and milk over potato mixture. Sprinkle top with Cornflakes, gently crushing cereal with your hand slightly as you sprinkle them over top.
Bake uncovered for about 45 minutes.