Line a 9x9 (or 8x8) inch pan with foil. Spray lightly with cooking spray. Place a number of unwrapped candy bars into the bottom of the pan, leaving room between for brownie batter to fill in. Prepare brownie mix according to package directions. Pour brownie batter onto candy in pan, then place another layer of candy on the top of the brownie batter. Bake according to brownie mix directions. Allow to cool completely, cut and serve.