Line a 13 by 9-inch cake pan with aluminum foil and spray with baking spray.
Baking spray with flour
Prepare the brownie mix using the egg, vegetable oil, and water according to package directions.
1 box Ghirardelli Chocolate Supreme Brownie Mix, 18.75 ounce size, 1 large egg, ⅓ cup vegetable oil, ¼ cup water
Using a spatula, spread half of the brownie batter into the prepared pan. It will be a thin layer.
Open the candy and place about 2 ½ candy bars on top of the brownie mixture, covering it completely. Cover the candy bars with the remaining batter, spreading it with a spatula.
3 bars Hershey milk chocolate bars, 7.56 ounces each
Bake according to package directions. I started with 35 minutes and watched them from there. Remove them from the oven and let them cool completely in the pan.
Using the edges of the foil, lift the brownies out of the pan. This makes them easy to cut into squares.