Heat oven to 350°F. Spray 10-inch ovenproof skillet with cooking spray.
In medium bowl, stir cookie mix, butter and egg until soft dough forms and then mix in some cut KitKat pieces. Spread dough evenly in skillet, pressing to flatten and cover bottom, then break and cut more KitKats and add on top.
Bake about 25 minutes or until edges are light golden brown. Do not overbake; cookie will continue to cook once out of oven. Cool 5 minutes on cooling rack; cut into eight wedges and serve
